PSU Won't Start

I have an Ultra X-Connect 500W PSU.  I really love these things, but this one has an odd problem.  When I hit the power switch on the case, the LED's flash and the fans turn a few times and that's it.  No power-up.  I turn-off the switch on the back of the PSU and turn it back on several seconds later and repeat.  This extremely-frustrating process can go on for a few seconds up to 15 minutes.  It does eventually fire-up and when it does, the system runs flawlessly for hours.  I had it on all afternoon and it worked perfectly.  I can reset the computer with no problem, but if I shut it down, it will not power-up without repeating the same misery.

Is there anything I can do to fix this, besides putting in a different PSU.  I'll throw an old, nasty PSU just to get by, but I want to fix this Ultra PSU.  I know the Ultra is WAAAAAAAAAAY under-stressed. 

are you sure its a psu problem itself?

maybe the powerbutton is not that great anymore? you could try to connect the reset swith to the powerswitch header on the board, and use the reset switch to fire it up, maybe its just the power switch of the case it self.. its allways worth a try. then you know for sure its a psu or mainboard problem. if that does not chance anything

I'll give that a shot.  I didn't have these problems until the moment this PSU went in this case, so it would be a really convenient time for the power button to stop working. 

I did unplug the power button and just jumper the connection on the mobo with a pen.  Still nothing.

I don't think it's a bower button issue.  I've discovered that if I discharge the PSU, I can get it to start easily after reenergizing it.  If I turn off the switch on the power supply and hold the power button for 10 seconds, I can then turn it on and fire the system up, no problem.  Once it is running, it will run all day if I want it to. 

Also, Microsoft must have taken their XP activation servers offline.  Too bad.  I was going to activate a fresh installation of Windows XP.  I was able to call the automated hotline and activate that way.  I hope they don't take that away from people.  XP was (and still is) a great OS.

Sorry for my late ansewr, But i would say RMA the psu. then, seems like there is something wrong with it.