Power supply keeps dying - 3rd PSU within 1 month

I don't think it's an issue with the line voltage - the power bar / surge protector should take care of any power spikes. Plus I have a lot of other stuff plugged into the same bar (as mentioned above) and haven't had power issues anywhere else in the house. Either way, I will definitely check it when I get home.

I'll also look into a new PSU. Just waiting to hear back from Thermaltake RMA - I've developed a relationship with them over the past month!

I measured the incoming voltage and frequency at the wall outlet and power bar outlet with a professional multimeter (Fluke). I was getting 122VAC at 60Hz, stable (+/- 1VAC, 0.01 Hz). No noticeable fluctuations with incandescent lights when major appliances are powered on. Also heard back from Thermaltake RMA who said my system is probably underpowered at 500W and I need at least 600W. Checked the graphics card specs and it recommends 400W minimum system power, but that doesn't take into account my extra HDD's and RAM...

One other possibility I've heard about is a grounding issue with the MB. Does this seems likely?

Either way, I'm looking at getting a new power supply (XFX PRO Series 750W or Thermaltake Toughpower 750W) and a new surge suppressor (APC P11VNT3 Performance SurgeArrest). I'm ordering the parts online and should have them within a week or so (using my laptop in the meantime, as I have been for the past 1-1/2 months). Thanks everyone for the advice and tips, and I will let you know if this resolves the issue.

I know it's been a month since the last post, but I've been a bit busy and haven't had the time to deal with this. The issue still isn't resolved and I'm thinking it's less and less likely to be a power issue. Thermaltake RMA got back to me and turns out I've been testing the PSU wrong... I forgot to jumper the ground (green) and negative (black) wire on the MB connector so the PSU wasn't powering up when I tested it. With the jumper in place, the PSU works fine and all voltages check out. The HDD's and DVD drive will power up fine, as will the GPU.

However, when I plug the PSU into the MB (24 pin connector) and the CPU (4 pin ATX), nothing happens. I tried this several times (unplug everything, plug it back in and try to power on) and then, randomly, my computer turned on! Everything seemed fine and then it "died" again when I started using it. Checked the PSU with jumper in place and power is ok. Plugged it back into the MB and nothing...

Eventually I got the computer powered on again and tested the RAM over several days using the Windows 7 memory diagnostic, SiSandra, and Memtest+ x86 (multiple passes on each) - neither detected any errors. I plugged everything back in (HHD's, GPU, DVD) and stress tested using SiSandra - no errors detected on anything. Started using my computer again yesterday for the first time in a month and it "died" again. PSU is ok and powers up when jumpered, but won't do anything when plugged into the MB. So I disconnected the PSU, waited 30 min or so, plugged it back into the MB and it powered up.

This is frustrating because I don't know what can be causing this. Right now the computer is powered on but I'm not using it. The GPU is removed, but everything else is connected. I've also checked the MB stand-offs to make sure I didn't miss any or have any extra ones connected. The unused ones don't have any shorts that I can see either.

Still think this is a PSU issue? I'm leaning more toward MB or MB/GPU/RAM compatibility, though I don't know why it would have worked for over 2 years without any issues. One other thing is that the computer always "died" when I was on YouTube. I don't know if this is a coincidence or pointing to a GPU problem...