Computer Shutdown Problem

This morning, I had to check something on the computer, then as I was headed out the door I shut the computer down (usually I just let it hibernate). It did the shutdown properly, but as soon as it was turned off, the fans, lights, and keyboard click would fire up, then shut back off repeatedly, like a heartbeat. Holding the power button in for a hard shutdown did nothing. I pulled the power plug for about 30 secs, but when I plugged it back in, it was back into heartbeat mode. I ended up leaving it unplugged until I get home from work.

I haven't had any time to diagnose it yet, but I would like some kind of idea what to look for when I get to it. I am guessing the power supply went wonky? Anybody have any ideas?

Thanks!

Power supply.

That's what I figured. Thanks!

And it was the power supply. I got a Cooler Master Silent Pro, they really aren't kidding when they say silent. The difference from my previous one is incredible.