I Thought it Was Heat Related Too
Sorry, for not updating sooner - my work seems to never be done! LOL
I did suspect heat at first, however, I'm now confident it is not - I've left ABIT EQ temperature monitoring utility running and none of the temperatures get much above 30 Celsius, even when the problem re-occurs.
I have swapped the keyboard and mouse for ps2 varieties and still got the problem - drivers?
I have also had it lock up in the BIOS screens when viewng the BIOS temperature monitoring screen for a long time.
Operating system is Windows XP Pro SP2.
I've today managed to spend some spare time on it and reset the BIOS (due to the lock up when in BIOS screens) as per the user manual - power off > power cord out > CMOS jumper setting changed > discharged for at least 1 minute > jumper reset > power on.
I have a bootable Fedora disk. Will give it a go, although I don't hold out much hope due to the lock up when viewing the BIOS.
Will also try to get task manager to run next time - there does seem to be disk activity when it occurs.
Thanks for the input so far - esp. Gore and nihil :)