Maximum PC

I have a PC I built myself about 3 years ago with the following components:
Antec 200 case
Cooler master silent pro 600 ps
I7-920
Asus P6T

I've run into an odd problem the last few weeks after an abortive attempt to put in a new video card (I eventually reverted back to my 5770). Every few days, when I hit the power switch, my fans will start to spin for maybe a second, and then slow down and stop. So power is coming on and immediately going off again. And after an attempt or two, nothing happens at all. It's a bit like a car where the battery has run down and the engine starts to turn over but just gives up.

I've opened up the case and unplugged and replugged power connectors and eventually gotten it to power up but it's not clear to me that anything I've done has actually had any effect. Once it does run, it will run flawlessly for hours, no problem. And the problem doesn't happen every time I try to power up, it will happen every few days.

My first thought was that somehow the power supply was screwed up, and I actually ordered a new one, but the fact that the PC will work fine once it's running makes me think that it's not a power supply issue.

Any idea where to go from here on this problem? I don't have enough components lying around to just randomly swap things.

thanks - Dave

Funny... I posted this over a month ago and apparently it just got approved to go on the forums. Anyway, problem was just a loose connection between power supply & motherboard, unplug/replug fixed it.