Boot up issues, pls help

Here's what happens. When I power on, the fans spin up, and then stop. A couple of seconds later, then spin up again and stop. I pulled everything out and put it back in piece by piece, and it powered up again. This time it booted fine. Couple days later there's a windows update. (Running Win2K Pro) Installed and rebooted. Not a good idea. Would get past windows splash screen and stop before login screen. So I bring it to work with me to work on it in my spare time. Then it's doing the fans spin up, stops, rinse, repeat. I take it back home, unplug my cd rom and it boots. Plug my cd rom back in, no boot. Unplug my old HDD, and it boots. So I'm thinking something is wrong with the PSU (500W dual rail, more than enough power). (System is about 2 years old) Anyway, I reinstall windows, and everything is working fine. I'm on wireless and the stupid driver cd needs flash player to run. So I bring it back to work this morning, and now it won't boot again.

I'm thinking it's a short somewhere. Any ideas? Specs should be in my sig.

It's not OC'd anymore. Hasn't been in a while.

Stuff not in Sig: X1950Pro, 3GB GSkill, 500W (PowerMax I think) PSU