All games cause system crash

Hi. I have a strange problem where playing any game will cause my system to hang.

Games including Test Drive Unlimited, GTA San Andreas, within a few minutes of starting gameplay all video and audio will stop and PC goes into sleep-like state with fans slowed. (doesnt shut down or reboot, have to power off)

Im sure the problem lies in the hardware, as I have since done a clean reinstall of Windows, tried several different versions of video/audio drivers and such.

PSU is brand new and tested, not the cause, same with the memory.

Also cleared CMOS, no help.

If anyone has any other ideas let me know.

thx

PSU Coolermaster 850W
Mainboard Asus A8N-SLI Deluxe
CPU AMD Athlon64 4000+
Memory 2x 1GB DDR400 (tested)
Video GeForce 6600GT
Storage 2x 80gb Sata Raid0
2x 200gb IDE

Note: 3dmark causes same system crash within seconds of starting tests.

 

What are your temperatures looking like? I have the same mobo and it likes to run hot so make sure that everything is getting proper cooling.

 

forgot to mention that, all temperatures very low, the chipset fan replaced with a passive cooler long ago. lots of case fans

 

Have you run a memtest?

 

yes, memtest reported 0 errors.

have also tried alternative ram/alternative slots

 

Have you tried taking everything apart and starting from scratch? Maybe you are having grounding issues or something isn't seated just right.

 

yes, had it all out on the desktop, no difference. has been working 2 years or so before this