I'd be very surprised if the processor were overheating. Even when running Prime95 on all four cores, the highest temperature was never over 65 C, and even that was rare. Crysis is demanding, but it doesn't use up all of all four cores. It's been hotter lately than it was when I ran the test with Prime95, but I've been keeping SpeedFan running while gaming to track peak temperatures and never saw any alarming CPU temps. I don't think an overheating CPU could have been responsible for some of the odd behavior (specifically, the keyboard lights). What typically happens when a CPU gets too hot, and at what temperature does it do it?

I have a spare 400 W PSU installed in my old computer, but I wouldn't trust it to supply enough good power for this new system, especially under load. Perhaps it'd be an option if I removed a video card and a hard drive. I figure my computer takes four or five hundred watts when under 100% load. I can send back the faulty part and have it replaced, but I'd like to make sure that that's the part before doing so. I'm hoping it's the PSU, as that'd be far less of a hassle to replace (especially since it's modular).

Any ideas how I can narrow this down without having a spare PSU to try?