ok so here's the deal, i got on my computer in the morning and it was working just fine, then i shut it down and i left for about 3 hours, when i came home i turned on the computer and it won't turn on, i know its not the power source because you can hear all the fans and stuff start to rev up but then it just stops and the power light just blinks. my computer is a dell dimension 4600 w/ win xp service pack 2, please someone help