Computer Fails to Boot
Here are some points worth considering when a computer fails to boot (they
are not presented in any particular order):
- If your computer has recently been moved, the CPU might no longer be
seated properly.
The CPU always has a large heatsink clamped to the top.
Heatsinks are often heavy, so if the computer is not handled carefully,
the heatsink can swing to one side, tilting the CPU and pulling some
of its pins on the opposite side out of the socket.
If you remove the heatsink from the CPU then you will probably need to
apply new thermally conductive compound between them.
To avoid this, try to release the zero-insertion-force (ZIF)
socket’s clamp without removing the heatsink, make
sure that the CPU is fully seated in the socket, then
clamp the CPU back in place.
- UK mains electricity is 230 Volts alternating current, so if the
computer’s power supply is capable of accepting either 230
Volts or 110 Volts, make sure that it is set to accept 230
Volts.
- Never assume that the power supply is working properly just because it
lights up a green LED.
Also, if you test the DC voltages being produced by the power supply and
they are all as expected, this does not mean that the power supply is
capable of producing the required levels of current.
It is not simple to test a power supply without using a dedicated power
supply tester, and they are quite expensive.
- Clear the CMOS memory by removing the CR2032 (or similar) battery from
the motherboard then either waiting for the settings to be lost, using
a jumper on the motherboard to wipe the settings, or short-circuiting
the positive and negative battery connections with something that is
electrically conductive.
This will get rid of any corrupted information, and delete any settings
associated with aggressive overclocking.
If you have set the system up to save time by not doing the usual
Power-On Self-Test (POST) every time the system starts, this will
make the system go back to doing the usual POST procedure
whenever you try to boot the system.
- Remove any non-critical devices, such as optical drives, that drain
power unnecessarily as a matter of course, or may even have
internal short circuits that divert power that should be
used to supply the essential components.
- If the computer was moved shortly before the failure to start up,
mechanical stress might have caused a microscopic crack in one of
the circuits on the motherboard.
There are two simple methods you could try to test for this possibility.
One is to flex the motherboard slightly upwards or downwards using some
material that is not electrically conductive, to see if any potential
crack closes and the system will then boot.
Another is to warm the motherboard with a hot air gun to see if the
system will boot when all the solder tracks on the motherboard have
expanded and closed any microscopic breaks.
Make sure that you do not use a setting high enough to melt solder,
as that couse cause irreparable damage.
These methods will not, of course, reveal the location of any small
break, so the motherboard would probably still be a write-off.
- Temporarily remove the motherboard from the system to see if any small
pieces of metal from elsewhere in the system have come loose and
become stuck underneath, grounding the motherboard against the
computer’s metal casing.
If that is not the problem, you could take the opportunity to try
fitting another motherboard before replacing the original.
- If the motherboard has been manufactured using electrolytic capacitors,
rather than durable capacitors, check all the electrolytic capacitors
to make sure that they do not have bulging tops or appear to have
leaked.
Having said that, most high-end systems are now built using only durable
capacitors, so this problem usually only affects old or cheaply made
systems.
- Many motherboards are fitted with LEDs that light up in specific
patterns to indicate significant problems, such as insufficient
power or bad memory modules, so check the meaning of any LEDs
that are lit up.
Some systems produce patterns of beeps from a simple speaker to
indicate problems, so if you can hear any beeps when trying to
start up the system, find out what they mean.
- Even if your system does not start up properly, the fans may still spin.
However, the fact that the fans spin means very little.
If the CPU is broken, one or more RAM modules are bad, or even if the
motherboard has failed, the fans will probably still spin.
- Disconnect then reconnect every single connector in the system.
- Remove all RAM modules from the system then try booting with just one
module in the first available slot.
In case that RAM module has gone bad, you can then try another one in
the first preferred slot.
Just in case the first RAM slot on the motherboard has gone bad, you
can repeat the process using the second preferred slot.
You should consult the motherboard manual to find out the first and
second choice positions to try when only using one RAM module.
- If your system has a graphics card and also built-in (integrated)
graphics on the motherboard, try removing the graphics card.
It is possible that the system is actually running, but you cannot see
that it is because there is no graphics output.
If the system is set up to run the Power-On Self-Test (POST) every time
it starts, which is normal, you should hear a single beep from the
built-in speaker at the end of a successful test.
You can also try using an alternative output from the graphics card.
Some graphics cards have DisplayPort, HDMI, DVI, VGA outputs, etc.,
so try using one of the outputs that you do not usually use.
Also remember that graphics cards often require supplementary power
connectors and will not work by simply being plugged into the
motherboard, which cannot supply enough current on its own.
- If your computer has a traditional hard drive, disconnect it and try
turning the system on.
See if you can get the UEFI / BIOS screen to appear.
This is the screen that on many computers shows a manufacturer’s
logo and other basic setup information before anything else, such as
the Windows logo for example, appears.
- Make sure that the computer is not refusing to boot simply because the
case is open.
Some computers have intrusion detection systems.
Bootable CDs / DVDs that are Useful for System Repair
Problems Booting from CDs / DVDs
If you are having trouble booting from a bootable CD or DVD, and keep
getting a Blue Screen of Death error with stop code 0x7B, go into the
BIOS and switch off AHCI (the Advanced Host Controller Interface).
The CD or DVD will probably then boot, but remember to switch
AHCI back on again later.
Booting from USB Flash Drives
Some systems, such as netbooks for example, do not have CD or DVD drives,
but you can usually boot these systems from a USB flash drive instead.
You can use ‘USB Image Writer’ to create bootable USB flash
drives on Linux systems and ‘UNetbootin’ to do the same thing
on Windows systems.
One advantage of USB flash drives is that they boot faster than optical
drives.
Another is that you can easily re-write them with new versions of bootable
images without creating a pile of obsolete media.