I've had this problem for several months (since last spring) and I am now just sucking it up and not playing too many games, but I thought I'd try one last time to hope someone has a bright idea and solves my issue.
The Problem: My computer randomly shuts itself off. No BSOD, no restart, no warning, just instant powerdown, as though I would unplug it.
Details: Originally, when I was playing a lot of Europa Universalis III, it happened almost exclusively when I was playing the game. Now that I no longer play it, or really much of any games, it happens with seemingly zero consistency. Sometimes once a day, sometimes more. Always when running Windows (never before boot)
At one point, I unplugged my front USB ports from the mobo, and I thought the issue went away, but it obviously didn't. I think the frequency may have reduced, but I'm not even sure about that.
Things that it's NOT:
Power supply - tested with volt/amp meter, also tested with alternate supply
Power surge - I've moved across the country twice, so it's definitely not from the wall outlet.
Video Card - tested with alternate, same issue
CPU overheat - temperatures are fine: 30C idle, 40C full load, definitely not the issue
GPU overheat - Vid card is at a stable 68C, also tried different card
CPU: Athlon X2 4200+
Mobo: ABIT AN8 Fatal1ty
Vid Card: BFG GeForce 6800GTOC
Memory: 2x 1GB Corsair XMS memory
PSU: OCZ Modstream 520W
CPU cooling: Zalman 9500
Case: Lian-Li PC-65
HDD: 160G SATA, 200G IDE
OS: Win XP Pro sp2
All drivers up to date
Throw any thoughts or questions at me that you'd like. I've attempted to troubleshoot this issues on several forums a couple months ago with no luck, so I'll try not to snap at anyone for asking a question I've heard several times before. Just please read all my details and don't question my "things that it's NOT" section too much
Thanks in advance for tips/suggestions/questions.