New build not working

[brainwave]

I would appreciate any help on this.
I just built a new machine which was working fine on initial boot. I was able to load WinXP Pro. I was able to update to latest BIOS. I reset RAM timing from 5-5-5-18 to 5-5-5-12. The machine was on for about 4 hours. I benchmarked with 3DMark05. I left the machine on and went out for 2 hrs. When I returned, the machine appeared off. The power LED on the case was flashing (it should be steady). The monitor had no signal. The 2 case fans (plugged directly to the PSU) were running. The PSU fan and the CPU fans were not working, but every few seconds both fans "twitched". The HD was not spinning. The green LED on the MD was on.

I shut down the power, then turned power back on. Same as above. No go. I have built about 20 machines and never encountered anything like this. I suspect the PSU since the case fans should not be spinning when the machine is off even if the PSU switch is on.

Here is the rig:
PSU: Thermaltake TR2-500 watt
CPU: C2D E6600
MB: Intel G965WH
RAM: Corsair Twin2x 6400 5-5-5-12
HD: Seagate SATA 750 gig
Vid: Visiontek ATI X1300 PCIe x16.

Help! thanks

 

[brainwave]

Update: The problem is not the PSU. I just replaced the PSU and the same problem persists. I am assuming the MB when bad but that seems so unlikely.
Any thoughts would be appreciated.

 

[HauntFox]

My first guess would be a bad motherboard. But you should probably try other things before replacing it, like clearing the CMOS, and if you have any spare parts, try those.

 

[brainwave]

Thanks Hauntfox.
I tried clearing the CMOS with the jumper, but no luck.
I agree the MB probably went bad and I will RMA it. Even if I got it working now I would not trust it. It just seems strange that it stopped working after running fine for 6 hrs.