anon@anon.com wrote:
[...]

I tried the Prime95 torture test and it rebooted within 2 minutes.
Yikes!  I ran Memtest86+ for 2 hours, 7 passes, with no memory
problems.

[...]

Looks like memory and light useage is ok. Intensive loading and it fails...

Most likely you've got CPU and possibly also motherboard cooling problems. Clean heatsinks and fans? Heatsink properly mounted on heat conductive grease?

If the heatsinks and fans are clean, then take the CPU heatsink off, clean it and the CPU, and reinstall with heatsink grease. Don't trust assemblers... I've found heatsinks mounted dry (and very hot) on brand new machines!

Otherwise, is your PSU or capacitors on their last legs?

Or have you been BIOS tweaking and messed up the voltages?

Good luck,
Martin