I post this in the motherboard forum because I've tried this with three different video cards and have gotten the same (or worse) results -- I suspect a motherboard issue.
Gigabyte GA-X58A-UD3R motherboard
Intel i7-930 CPU
6GB OCZ RAM
Radeon HD 5670 video card
1) Brand new build. Everything was going fine until I tried to install the video drivers -- then there was significant instability; the machine would turn off after a minute or so of loading up Windows 7. OK, maybe it's a driver issue.
2) Rebuild the machine, don't install video drivers, just use native Win7 generic driver. I can't get the screen resolution I want, but otherwise everything is great. I did some load testing of the CPU, no issues found no matter how much I threw at it for how long. Great.
3) Install graphics driver...same problem as #1. Sometimes it ran few more than a few minutes before shutting off, but it always died within ~15 minutes of normal use (web browsing, etc, no games).
Unload graphics driver by uninstalling the display adapter in Device Manager...and it's stable again.
I tried the manufacturer's drivers, including one version back, and ATI's drivers, including several previous versions. Same problem.
4) Here's where it really gets weird. I tried 2 other, older video cards...and it wouldn't even make it to the login screen before dying (turning off). I am now back to my original video HD5670 card with generic Win7 VGA drivers...not exactly where I want to be, but at least it boots up now and I can sort of use it.
What the heck is going on here???
I visually observed the motherboard during the boot-up-then-die process several times, and all fans were operating correctly, and no warning LEDs were lit.
I have tried putting the video cards in multiple different PCIE slots. Same problem in every slot.
Are there perhaps some PCIE settings I'm not aware of? I've tried the Load Failsafe Defaults in the BIOS, no help there.
Any thoughts on what I'm missing? There's no VGA adapter built into the motherboard, so I can't take the video card out of the equation entirely...I'm out of ideas.