Hey, I just got my PC repaired (failing motherboard) but now after about 30 minutes of it being on, I shut it down and when I came back to turn it on it wouldnt start up. The loading light flashed for a second then went blank. The green light on my mobo is on but the fans are not spinning. I have an asus p5p800 mobo and a 450watt genuine psu..... what could be the problem????