Troubleshooting Boot Failure

[WhisperingClaw]

I recently rebuilt an older PC, and now it seems to randomly shut off during start-up. I'm thinking the new power supply may be defective, but I'd like to gather an opinion before I send it back. My trouble is this: Sometimes the system will load all the way up to the Windows login screen before shutting off (I have seen an error a few times, but it did not look like a STOP error message, I also can't retrieve any debugging or boot logs) and sometimes it will shut off with no error during loading. Attempting to boot into Safe Mode or Last Known Config does not work and also causes the system to shut off. In all cases, the system does not restart itself. So I'd like to know whether this is likely a power supply issue, an issue with Windows, or perhaps something else.
Thank-you!

Parts:
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Mainboard: MSi G31TM-P21
PSU: Cooler Master Extreme Power Plus 500W
CPU: Intel Core2Quad Q6700
GPU: nVidia GTX 550Ti
RAM: Corsair XMS2 4GB DDR2
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OS: Windows XP Professional SP3

 

[dragonlord12832]

The computer shutting off is typically attributed to either over heating over an unstable power source. Go ahead and send that power supply back. By the way, did you check the reviews on this PSU to see if anyone else had problems?