i had that problem with a AMD sempron, it would start up for a second then die. if i left it for a few minutes it would boot, then die. i was frustrated and bougt another PSU. worked fine for a few days, then same prob. both PSUs were good. found out : the mobo was touching the case, nd it was grounding it, solved : take mobo out and set it on the floor, and connect everything to it, try it, if it works then ya got a bad case, (if ya want that case put some paper or something in the back to un-ground it.