My buddy cheyenne1212 from my first forum site had a similar problem and got it resovled.
HERES THE LINK

I starting to think it might not be shorting out. When it shut`s off the led light on the M/B stays on. which makes me think that it might be a connection or the PS.

Tru...........man I have about five of those laying around here. Hopefully you have a spare . It really might sound bad to you but I have heard worse try another one and post back..........Good luck

I'm having the same exact problem. The power supply is made by L&C Technology and I just replaced it with the same exact one (found it online for like $9). Everything seems to be getting power, just won't boot up. It's an ASUS mobo with a Pentium III processor. Could this be a bad/burnt processor or bad video card? Although, a bad/burnt P3 seems odd. I've never heard of or had to replace one before. That's all I can think of after taking everything out and reinserting it all. Anyone have any similar experiences or input?

my friend had the same problem, this solved his prob but it might not solve yours. there was a tanish plastic looking pin that was is the wron slot. he moved it up one or down one and it started up perfectly. the pin had something to do with restarting and it wouldnt start with it in the wrong place. it would go on for about 4-7 sec then turn off. http://www.trustedreviews.com/images...0-overview.jpg
heres a pic of the pin, im not sure if you can see it too well but the pin im talkin about is in the top middle of the pic and directly under the small red and yellow wires.