|We will address five basic scenarios in
this guide, ranging from a stone dead system to a lack of functionality,
such as a modem that won't connect. While these procedures will uncover
most assembly errors, there is often no way to isolate a dead component
without having other known good parts to swap out. In the world of
professional PC troubleshooting and repair, the "Swap 'til you drop"
strategy is still the most common troubleshooting technique employed.
Swapping components requires no expensive diagnostics software or
hardware, and is usually the quickest way to isolate a problem. Another
reason to steer clear of specialized diagnostics tools is that they are
geared to identifying problems with sub-components that can't be fixed
anyway. Finding out exactly which address is bad in the system RAM or in
the cache memory of a drive or motherboard is of little use when you'll
have to replace the whole assembly anyway.
If you smell a burnt electronics odour at any time,
you have a blown component and should not attempt powering up again
until it is found and replaced, and the cause of the failure is
determined. Just give call 08700 116550 and we can arrange
an onsite engineer to visit you. Remember that the information
given here must be considered a general guide and if you do not feel
confident to do it yourself, do give us a call to arrange an appointment
with a service engineer. OnCallComputerDoctor.co.uk cannot be held
responsible for any problems arising from misapplication of the
Where to start:
Scenario 1 - Stone Dead.
You switch on your new system and there are no signs
of life; the power supply fan doesn't turn, there are no sounds, no
- Power supply - Make sure the power cord is fully
inserted into the power supply, that the override switch on the back
of the supply (if so equipped) is turned on, that the voltage switch
is set correctly. Don't neglect to make sure the wall socket you are
plugged into is live by unplugging the computer and plugging in a
radio or lamp to check.
- Motherboard connections - Recheck the motherboard
documentation for the proper connection of the leads from the front
panel power switch. Don't settle for just looking at the switch
connection to the motherboard; remove the lead, check that the
terminal block matches the documentation then reconnect it. Undo the
main power supply connection to the motherboard (this requires
pressing in the clasp as you pull gently on the connector), inspect
the connectors for damage, and reconnect.
- Bad component - Disconnect the power cables and
ribbon cables from the drives, one drive at a time, retrying power-up
after each drive is disconnected. Without reconnecting the drives,
remove each adapter card (leave video for last) one at a time,
retrying power-up after each removal.
- Motherboard components - Remove and reinstall
memory DIMMs or RIMMs, inspecting for physical damage. Remove and
reinstall the heatsink and CPU, double checking the CPU fan is
connected to the proper terminal on the motherboard. Never attempt to
power up the system without the heatsink installed.
- Switch - In extremely rare cases, the power switch
on the front panel may be faulty. You can use a continuity checker or
Ohm-meter to check the switch, or you can carefully, carefully, take a
screwdriver with an insulated handle and momentarily short the two
pins where the switch lead connects to the motherboard. Although the
switch works on low voltage, you may be startled if and when the
machine comes on and rake the screwdriver tip across to motherboard,
so don't try this unless you have some experience working with live
- Remove the motherboard from the case and check for
loose screws, extra standoffs, and anything else that could cause a
short circuit to the motherboard circuitry. Reinstall the motherboard
in the case and reinstall the video adapter, then try powering up.
If you still have no power, than the problem is most
likely a defective power supply or defective motherboard.
Scenario 2 - Power comes on - Screen
- Monitor - Make sure that the monitor is plugged
into a good power outlet by switching wall sockets with the power
supply cord. If the power cord is not permanently attached to the
monitor, make sure that it is fully inserted in the socket on the back
of the monitor.
- Connection - Remove the monitor connector from the
video card and inspect that none of the pins in the are bent over.
Note that some missing pins in the three row high density connector
- Video Card - Remove and reseat the video adapter,
making sure that the hold down screw doesn't cause the back end of the
adapter to lift partially out of the connector. If the video adapter
is populated with removable DIMMs, remove and reinstall these.
- Defective or conflicting adapter on bus - Remove
any other adapters installed, one by one, rechecking power-up after
each. Don't forget to unplug the power supply or turn off the power
strip or override switch before each removal.
- Double check the motherboard documentation for
overlooked CPU selection switches or jumpers settings. Depending on
the motherboard used, CPU selection may be automatic.
If you still have no live screen, the problem is
likely defective hardware. Make sure that the case speaker is properly
connected to the motherboard as per the motherboard documentation. If
you hear a series of beeps, note the number and sequence, as they will
pinpoint the defective component. The motherboard documentation or
manufacture web site should give the codes. If no beeps sound, the most
likely candidates are a dead monitor (easily checked by connecting it to
another system), a defective motherboard, or a defective power supply.
In some rare instances, you may have a bad CPU, RAM or a bad video
adapter, and still not hear any beep codes.
Scenario 3 - Screen comes on - No
- No onscreen messages indicating boot failure.
- Enter CMOS Setup by following onscreen
instructions (usually by hitting the <DEL> or <F1> key). Select the
CMOS option to "Restore Default Settings" or similarly phrased
option, save and reboot. Note: If you cannot access Setup, double
check that the keyboard and mouse connectors aren't interchanged. If
you still can't access setup, disconnect power and remove all
adapters except the video and disconnect the drives. If you still
can't access Setup when you reconnect power, you have some defective
hardware, most likely the motherboard, RAM or CPU. These core
components should always be bought from the same source to simplify
- If there are still no messages indicating boot
failure, enter CMOS Setup again and make sure the CPU speed setting,
the bus lock frequency and the IDE interface speed don't exceed your
- If the system hangs at "Verifying DMI Data Pool",
it is usually a motherboard or IDE device problem. Disconnect your
IDE cables from the motherboard and see if you can get as far as a
"Drive Failure" or "No Boot Device" message. If not, the motherboard
will probably need replacing, though you can try discharging the
onboard battery first by using the jumper setting in the motherboard
manual for disabling a forgotten password.
- Missing operating system or no boot device message.
- Check that the IDE cables are connected to the
drives and motherboard properly by removing and reinstalling them.
Make sure that the power connectors to all of the drives are
properly installed. Make sure that the Master/Slave jumpers for the
drives are installed properly
- Tries to boot CD and fails - Strangely enough,
some high speed CD drives take so long to get up to speed, that the
BIOS (motherboard logic) gives up on them before they get there. If
the screen displays a message like "Insert CD and hit any key when
ready", eject the CD tray, then push it back in, but wait until you
hear the drive spin up before striking a key to continue. It make
take a few efforts to get this right if it's going to work.
- Check the operating system CD is readable in
another system, and don't try using pirated operating system
software on home recorded CDs.
- Enter CMOS Setup and re-arrange the boot sequence
so that the CD-ROM or the IDE channel it is connected to is selected
as the first boot device. This shouldn't be necessary, but it will
help if a previous attempt to install the operating system failed,
but left the hard drive looking bootable to the motherboard.
- Simplify the system by removing any additional
drives so all you have left are a master hard drive on the primary
IDE channel and a master CD on the secondary IDE channel.
Scenario 4 - Boots - Locks up during or
immediately after operating system install
- Unplug the power and remove all adapters except the
video adapter. Install the operating system. Next install the
motherboard drivers from the CD that shipped with the motherboard, and
the video adapter driver from its own CD. If the operating system
still won't install, check with your parts vendor or the operating
system vendor (Microsoft for all Windows versions) for compatibility
issues with your components.
- Install any other adapters one at a time, reconnect
power and reboot, allowing the operating system to deal with them
- Make sure that you are using the approved cabling
for any high performance parts such as Ultra 66 or Ultra 100 hard
drives, since communications breakdowns at high speeds are likely to
show up under the load of operating system installation.
In some rare cases, operating system installation may
fail repeatedly because a borderline component is suffering a heat
related failure as the system warms up. This is extremely difficult to
troubleshoot without parts to swap out, and if you bring the parts back
to the point of purchase, it may be hard to convince the vendor that the
problem isn't in your imagination. Go through the steps related to CMOS
Setup in Scenario 3, and document all the troubleshooting steps you go
through for the vendor. Try reinstalling the operating system several
times before concluding that you have a heat related failure.
Scenario 5 - Boots and runs
If your operating system installation goes smoothly,
but you have trouble accessing a particular device, the problem is as
likely to be software as hardware. Extensive software troubleshooting is
outside the scope of this book, but we will mention some of the key
points you can check in Windows operating systems.
- A) Floppy Drive
- If the activity light on the front of the floppy
drive stays lit all the time, the ribbon cable on the drive or the
motherboard is probably backwards.
- If the drive is not detected properly by CMOS
Setup or recognized by the operating system, either the ribbon cable
or power cord are partially or improperly connected, or the drive is
- For any problems reading or writing specific
floppy disks, either the drive is bad, the disk is bad, or the drive
that wrote the disk is incompatible with the drive trying to read it
due to head alignment issues.
- B) Hard Drive
- Any message indicating a hard drive read or write
failure is a hardware error. Try replacing the ribbon cable, making
sure you use the newer 80 conductor type.
- Isolate the hard drive on its own IDE channel,
moving any other drives to the secondary channel on their own cable
or temporarily disconnecting them.
- If the hard drive is excessively noisy or makes a
continual clunking sound, it has suffered internal damage, and odds
are even an expensive data recovery outfit won't be able to help.
- If the errors persist, either the drive or IDE
controller is bad. If you can disable the motherboard IDE controller
in CMOS (both channels), you can try substituting an inexpensive PCI
IDE controller before giving up on the motherboard.
- C) CD or DVD Drive
- If the drive has trouble reading a particular
disc, try wiping off any fingerprints with a clean flannel shirt.
Note re-writeable discs written in CDRs and DVDRs are often
unreadable in other drives.
- For continual read errors, try all of the steps
for hard drive troubleshooting; new IDE cable, isolation, swapping
- If you can't play music CDs even though your
speakers work with other computer sounds, the thin audio cable from
the sound card (or motherboard with integrated sound) to the 4 pin
connector on the back of the drive is improperly installed or
- If you record music CDs on your PC and they won't
play in your stereo, make sure you are using CDR blanks, not CDRW.
- If you have a CDR or DVDR and your write sessions
often fail, try recording at a lower speed, and make sure you are
using media certified for at least the speed you are recording at.
- Check that the phone line from the wall goes into
the modem jack labelled "line". Plug a regular handset into the
modem jack labelled phone. If you don't hear a dial tone, either the
modem or the phone line is faulty.
- In Windows, go to Control Panel > Modems >
Diagnostics > and click on "More Info". If your modem doesn't show
up in Windows, power down and try removing all of the other adapters
except the video card from the PC before rebooting. If Windows still
doesn't find your modem, try it in a different motherboard slot. If
Windows still can't find the modem, it is probably defective or
- If you hear the modem dial but the only thing
that happens is after a while the operator picks up, you are
probably dialling tone on a pulse system.
- If you never get connect speeds over 33K, contact
your Internet Service Provider with your modem information.
- If you connect between 33K and 53K but have
frequent disconnects, you probably have aging or overloaded local
phone infrastructure. Try another phone jack in your house in case
it is a just a poorly wired outlet.
- Sound Card
- Check Windows Device Manager to see if there are
any conflicts and be sure that the sound card drivers are installed.
If Windows didn't recognize the sound card, try powering down and
removing the other adapters except the video card from the PC before
rebooting. If Windows still doesn't find your sound card, try it in
a different motherboard slot, and if it can't find the sound card,
it is probably defective or incompatible.
- Make sure that your speakers are plugged into the
correct jack on the sound card, because the little pictures can be
deceptively similar. Make sure speakers with an external power
source are plugged in, turned on, and that the volume dial isn't
- If you have been using your PC for a while and
then lose all sound, the most common reason is the "mute" box being
mysteriously check in one of the innumerable mixer panels that
install with sound card software. Happy hunting!
- If the network adapter doesn't appear in device
manager, try powering down and removing the other adapters except
the video card from the PC before rebooting. If Windows still
doesn't find your network adapter, try it in a different motherboard
slot, and if it can't find the adapter, it is probably defective or
- If the card looks healthy in Device manager but
you can't connect to your local network, check all the software
protocols and identification settings in Control Panel > Network.
For home networks, getting the Workgroup name wrong is the most
- If you are sure you have all your software
setting right by comparing them line for line with another PC on the
network, you have a cabling problem. Almost all small networks are
wired for 10/100 BaseT, but the cables are often built incorrectly.
10BaseT and 100BaseTX use four conductors in two pairs in an RJ-45
connector, 1&2 and 3&6. Some other standards use all 8 wires, but
the important point in every case is that 3&6 must utilize a color
coded pair, something many cable makers still neglect.
- If the screen seems jumpy, particularly from a
distance, it could be the monitor itself. Another possibility is
interference from electrical equipment, like an external transformer
for speakers or other device resting near the speaker. In office
environments, electrical wiring in walls carrying high currents can
cause wavy interference.
- If you look at the screen out of the corner of
your eye and it seems to flash near the edges or bottom, the
vertical refresh frequency is probably too low. You can try a lower
screen resolution, or changing video modes, if the video card
software gives you that option.
- If you are missing a primary colour, check the 15
pin video connector to see if any of the pins are bent over.