AMD Phenom 965 Black
Thermaltake 850W PSU
1TB WD Caviar Black
4GB Corsair Dominator
Everything worked fine at first. POST'ed, installed winxp, played around for a little bit. Then I made a new account for myself, and rebooted the computer. Came up rather quickly to the Welcome screen, and I logged in with my name and password. The Welcome screen then got stuck on Applying Personal Settings, and then the computer blacked out. After hitting the power button again almost 30 seconds after it went off, nothing came on.
I unplugged and replugged the PSU. Immediately after pressing the power button on either the case or the inside power button, a few LED's flash, the fans come on for less than a second, then everything turns off, except for the 2 DDR_PHASE leds. Removing the ram, I powercycled and tried booting again, but the same thing happened. 1 sticked, same thing.
I've since pulled the entire setup out of the case and have it sitting in front of me. I've been unplugging and replugging components individually, together, and tried every combination of parts imaginable.
As a poor student who bought his first serious gaming rig, I don't have any parts to swap out and check, and no one around me does either.
My hypothesis is that it is the power supply. When I use a 5Watt 6Ohm resistor across the Green Line to Ground on the 20Pin connector, the PSU does the same thing it does when it's plugged into the board: powers on and spins it own fan for less than a second, then shuts itself off.
tl;dr Why would a computer work perfectly for about an hour, then shut itself off during a normal OS operation after POST and refuse to come back on?
If so, you'll notice that it's an older model that puts out a lot of Amps on the 3.3v and 5v rails. Newer models put out the majority of their power on the 12v rail where it's needed for modern systems. I would return your PSU for replacement and pick up a quality model from a known quality manufacturer like Corsair, Antec, PC Power & Cooling, Seasonic, or Enermax. Here's a very nice PSU for a good price:
Same thing happened as with his, unplugged replugged, 1 sticked, everything. Won't reach post. When mine f*** up however, it had ddr phase leds on only, and power and reset leds flashing. Then trying to start it again had the whole fans run for a split second then turn off, no phase leds or anything, and that's all it does now.
I even got another ultra 750 PSU, thinking it was a bad PSU problem because the PSU was the only thing not completely new in the build, but still not working.
Could it be not enough on the 12 v rail? Says it's running 45 amps on it, figured that would be enough.