Gigabyte GA-EX58-UD5 power cycling randomly

[bluedragon9r]

I've been having a problem with this motherboard lately, and I'm not sure where to start on the troubleshooting. Basically the system will boot and run fine for days at time. Then in the middle of use, it will shutdown completely. No errors, no BSOD, no event log..Shuts down like I'd just pulled the power cord. A few seconds later, it will restart by itself, and then go into a cycle of shut down, restart, shut down, restart. First restart, it doesn't POST, next one it gets past POST, next restart a little further, etc until it will finally boot again. Then it might run for days or hours before it does it again.

Not sure if the problem is the motherboard, memory or power supply.

Specs:
Gigabyte GA-EX58-UD5 (F9e BIOS)
i7 920 (tried stock settings and overclocked, no changes)
6GB Corsair DOMINATOR (1600, 8-8-8-24) (tried manual, default, and using the XMP profile)
ThermalTake 750W power supply
GTX 280 video card

The video card and CPU are both watercooled, and temps have never gotten above 39C.

I might have an old power supply to throw in the mix to test things, but I don't have any other memory, CPUs or motherboards. Any ideas where I should start? This one is really hard to troubleshoot since it seems to disappear for days at a time..

The only time I've seen this problem before is when I was overclocking things, but it's been back at stock settings for 2 months now before this started..

[ibleet]

Swap out the PSU to eliminate that and run Memtest overnight to see if your Ram is throwing errors. With an intermittent error like that, I'm thinking it may be memory related. It may be wise to pull out the memory and test each single stick with memtest.

[bluedragon9r]

I will try memtest this weekend..I tried a few things last night, reflashed the BIOS, reseated all the memory, and went back to default settings on everything. The only thing I noticed weird was the "power button setting" in the BIOS...normally that's set to the 4 second delay, but it was on "instant off". I'd have to laugh if this was caused by a bad power button.

After all that, I ran Prime95 and Furmark at the same time for about 4-5 hours, and everything was smooth. I left it running when I came into work this morning, so we'll see if it's rebooted when I get home. I hate troubleshooting random problems like this..too much false hope.

[pwcmed]

ibleet is probably right, the PSU is a good place to start. I have HTPC that had the same symptoms. I knew it was PSU when it would power up anymore.

[bluedragon9r]

Looks like it was a bad 24 pin power supply connector. I seem to be able to repeat the problem just by bumping or wiggling the MB connector. Now I just have to wait for the new PS to get here...or take the connector apart and fix it..