Power Gone in a Flash - What the Deal?

[Sammy5000]

Ok - So I am sitting at my PC doing some online banking (nothing hard at all) when all of a sudden, the computer shuts off. Not the monitor, just the computer. I try to turn on the computer, and get just a flash of power (barely 1/2 second and then nothing). At first, I am thinking the PSU. I have a beast of a PSU, so I plug it to a PSU Tester - all system good! I do my simple diagnostics (unplug power, unplug power connectors, flush power button, etc, etc). Try it again, no joy (1/2 second power - that is it).

I have a spare PSU (that I know is good) sitting around, and decide to plug that puppy into the mobo, and still, no joy on the mobo?

My next step is to take everything apart, as I am expecting there to be a short somewhere (although since I unplugged everything, my guess would be the mobo).

Any thoughts/recommendations/hints/suggestions you guys can share? Any help would be greatly appreciated.

Specs are below:
AMD Athlon 64 FX-55 (Stock)
DFI LanParty N4 SLI-DR (Bios Dated 6/23/2005)
Corsair TWINX2048-3200C2PT (1GBx2)
BFG GeForce 7800GTX PCIe
WD 74GB Raptors (2) - SATA
Samsung 80GB HDD - SATA
WD 120GB HDD - IDE
Plextor DVD-RW PX-712SA
Memorex DVD-Rom - IDE
Creative Labs Audigy 2ZS Gamer Sound
Dell 20"LCD
PC Power & Cooling 850 SSI SLI PSU
CoolerMaster Stacker Chassis

 

[Sammy5000]

Quick update - I just took the mobo out of the case. I just plugged in CPU, cooler, mem stick, and GPU for starters to see if any juice going to the board. I decided to use the spare PSU (PC Power & Cooling 550). I used the power button on the mobo and no joy, but just then, a loud POP and blue/gray smoke coming out of the PSU.

Now, remember, this was the spare PSU that was working before all this drama - and this was outside the case. Thank god I didn't use the 850. I am thinking something must have snapped with the mobo. Thoughts?

 

[ThePiston]

check for case shorts, then call an exorcist