Thanks for the feedback/suggestions.
I have downloaded 3dmark03 and prime test. So far it has run 3d mark 2 times without a problem with a score of around 14,800 if that makes a difference.
CPU temp is 35C, case is 34C and the hard drive with a temperature probe is at 40C. These are fairly typical temperatures and similar to when it reboots itself. I don't have a probe on the graphics card but I have checked the fan is turning. No dust problem yet as it is only about 6 months old since I assembled it.
System specs are
Athlon 64 - 3700
2 x 1 Gb DDR 400 Ram
ATI 1800XTX
Audigy 2 sound card
No other expansion cards
There are 3 hard drives and 2 dvds
It has 4 case fans attached to a fan controller.
The power supply is rated at 550W but is just a generic one.
It is running WinXP SP2
Other gamers installed ! Who has time?
I do have Oblivion installed which does give my pc a good workout so I will let the Mrs know I am under instructions to play it for a few hours
How do I check the event log?
It has run faultlessly until a few weeks ago when this problem started happening. It runs fine when not stressed but 8 laps is about as far as I can get in LFS. Is it possible so update to windows has installed itself and is causing the trouble or would that be more likely to cause a BSD rather than a reboot?
I will let you know if it survives running firstly 3d mark and then prime over night.
Thanks again
Maxim