Possible PSU Failure

[MotF Bane]

System was running fine for about 3 days constant (longest ever continual run). I checked it this morning, WCG was still running, although it noted the last two pieces had computation errors. Wandered off, and when I came back, put in my password (screen saver = password protect), it crashed immediately. Started to boot again, got past POST fine, made it until just before the Windows XP loading screen, and then it went back to rebooting. Shut it down using the power button up front, tried again, and got lots of fast chirps. Per my GA-965P-DS3 manual, that's power failure. I checked all of my connections to the motherboard, they're all solid. Am I missing something, or does that mean the PSU somehow killed itself? By the way, it's a Silverstone Olympia 650.

Edit:
Not power supply. I just patched together an Antec SP2 500 and a Dell 250, but it still gives the same chirps at POST.