Im after some general advice on how to start to diagnose a computer
freeze-up.

By freezeup, i mean mouse will not move, ctrl+a+d does nothing - power
off at the wall jobby.

An example. A computer that has worked fine for 18 months suddenly
starts freezing 3 - 4 times per day. Just to narrow down possibility
of corrupted drivers or system files, I format the hard drive and
reload windows (ME in this case). The computer needed a cleanout
anyway. Same happens, it continues to freeze several times a day.

I am suspecting hardware at this point (nothing else software wise has
changed and the hard drive has been formatted), but where do you start
- and at what point do you say, right - replace motherboard?

Look forward to some info.

apcs_uk-ga,

Thanks for the opportunity to answer this question!

CTRL-ALT-DEL is caught by the operating system.   It would be
beneficial to know what operating system you have, but if a complete
re-install occurred, it is unlikely the operating system is a problem
(although Windows ME has a notorious reputation for instability).  One
thing you don't mention is whether your drivers have changed, or
whether after your re-installation you updated the drivers on your
system, or whether the system was automatically updated somehow. 
Check these things first.

Given the description of your problem, I'd be thinking about memory
first and foremost.  If the video powers up and the BIOS seems OK,
it's more likely a memory problem.  I have seen similar crashes in
excessive heat situations - like, the processor fan stops working and
so the processor isn't getting cooled down, overheats, shuts off;
things of that nature.  The memory can be tested by a qualified repair
shop, or you can download applications which do exhaustive tests on
your memory.  I would try removing memory chips in your computer,
swapping them around, etc as a methodical approach to the solution.

The disk is unlikely, but possible.  If it were a disk error, I would
expect to be seeing many issues of data corruption in the freezing
situation which you describe, unless the error was on a particular
portion of the hard disk that was commonly accessed - say, for
instance, a swap file.  Again, a reinstallation would probably
highlight or at least provide some insight on this problem.

If the memory checks out OK and the processor fan is running, I would
look then at replacing the motherboard.  Motherboards do fail,
certainly.    If the computer is older than eighteen months this
becomes a slightly greater possibility, but many systems can run for
years without problems.  The memory is perhaps the most delicate
component in a machine when it comes to electrostatic or electronic
problems, and the situation you're describing leads me to believe
that's it.

I wouldn't replace the motherboard until you have replaced memory,
processor (if possible - on older models of machines replacing the
processor may be impractical and a motherboard+processor combo may be
cheaper or easier), and perhaps trying a brand new disk, but that is
less likely.  I rule out the video card since there are no odd
problems as far as the display goes.

Testing utilities - Commercial utilities are listed but free versions
should be available.

	http://www.uxd.com/wst.shtml (Windows Stress Test)
	http://www.pccertify.com/products/whatmem.htm (Memory testing
utility)
	http://www.memtest86.com/ (Memtest for x86)

Research methodology:
Google searches on lock-up, memory test, computer crash diagnosis
information, and personal knowledge

Good luck!

arimathea-ga
Researcher

Nicely summed up. I have changed the ram and had no problems yet.
Thanks for your time

Hi Apcs_uk-ga,

The motherboard and processor are normally the last things to go out.
There are a number of possibilities for this kind of behavior. One I
suspect is your hard drive, that it developed some physical bad
sectors. When the drive's reader tries to access the part on your
drive with the bad sector, it will try to access it over and over and
as a result, your system hangs.

Since you have formatted your drive already and have the option to
format it again because it's still empty, try to format it again and
have it scanned on another system using a disk utility such as Norton
Disk Doctor. That way, the bad sectors will be identified and tagged.

Another thing is overheating. Check your processor's fan if it is
still rotating or not. You can turn off your system and try to flick
and rotate the fan with your finger. If it rotates freely, well and
good. If it doesn't and it seems to be stuck, it's time to get a new
fan. If ever you'll buy a replacement, select the best fan available
in your area.

Best regards,
Feilong

I don't mean to confuse the issue even more, but I always suspect the
power supply first. Voltage instability will wreak havok on any
electronic system.