I had a problem similar to yours with my build powering off randomly. Turned out that the mobo was defective (either a short or fuse issue). Took me 6 months to nail it down and exchange the board for another. The defective board was a Gigabyte board with an AM2 socket. Got an Asus board, no problems since...
might be my situation, merkat. Everything in the computer works when the video card is out. I've got 2 PCIe slots and when I plug the video card in either one, fans spin for less than a second and it shuts down.
Does the video card require a PSU connection? Some do, and that will definitely send your board into conniptions if it isn't plugged in...
Edit: NVM, I just looked it up. No extra power required. My guess is that it's either a bad card, or a problem with the PCIe bus, and the motherboards power to the bus. That would be my semi educated guess.
Mellon, thanks for your input. Exchanged the motherboard today. MicroCenter let me do so after about 60 days, so big thumbs up for that. Good Lord, so glad I didn't mail order this stuff, I'd be here until the sun swallowed the earth.
I've got everything out of the case, started completely at square one. Only thing hooked up is the PSU, CPU & fan, 1 stick of RAM, 1 case fan. About two hours ago they all worked. I ate some dinner, came back, now nothing works. I'm at my wit's end...
Maybe it is the freaking PSU after all. Unfortunately, don't have a spare to test, or a voltage meters, etc.
It is starting to look like the PSU, isn't it? Have you got a buddy that can lend you one for an hour or so? If it works, it will put the issue to bed, once and for all.
I know it's rough, I just went through three weeks of troubleshooting with my new build. I do sympathize.
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