Hello Agamar,
This happens to me often -- maybr 50% of the time I make bios changes. Also, get this, let's say I install some software which requires a reboot, my system does not reboot but shuts off! I am pretty well convinced I have a bad boards...I have already got an RMA number, just waiting (and testing) while the new board is in transit.
I have tried swapping these components, trying to solve my crashing problem:
power supply
RAM
hard drive
CD-ROM drives
cables
removed sound card (audigy2)
No matter what I try the system straigt out shuts off during 3dmark, games, and sometimes just when surfing...we shall see what happens when the new board arrives.
DJM