PC turns on without CPU 4 pin plugged in. (Solved) With it plugged in the Blue Power LED and fans turns on for a second then turn off. Its my uncles HP Pavillion a250n. I've replaced the power supply with a new one, I've checked the MotherBoards battery (Its good), I've reseated and applied fresh thermal paste to the cpu and I've tired running the MB with nothing else connected to the PSU. I make sure the CPU fan is plugged in at all times. All in all the only way the PC will turn and stay on is if I don't plug in the 4 Pin to the MB which Obiviously I need to get it to boot. I'm not sure what it is? Perhaps a shortage somewhere? Should I just take everything out and put it back in? From what he has told me, its been running fine, then one day after he shut it down, it just wouldn't turn on. Ideas?