Desktop freeze; Hardware, Software?

[Shelagh Manton]

Over the past few weeks my desktop has frozen occasionally. The mouse
works but nothing else does. I've tried crt-alt-backspace to log in again,
I set up so that system monitor pops up, but needless to say it doesn't.
I read in the O'reilly LPI cert. book that crtl-alt-f2 sould bring up the
other ttys and work through things without X. But this doesn't work etiher.
I've scanned the log files in the hopes of spotting something different to
usual going on, but everything seems fine.
 Sometime the led at the front of the computer flashes and
sometimes nothing happens when its frozen. I've tried leaving it to
unfreeze, but have ended up just turning the computer off an restarting. 

Its got to the stage that I really need to find out what is going on.
May be its hardware? Possibly my gforce4 card is getting flaky in the heat?


Suggestions of what else to look for would be appreciated.

Shelagh