Sad to hear you are having PC problems. One thing that hasn't been mentioned yet is the windows install/hard drive (I know it's unlikely to be the source of the problem but better test it anyway since it cost nothing). Did you try to boot with a Linux live cd? Also, make sure you have unplugged all your USB devices. I've had PC not booting problems that ended up being caused by a defective USB device stopping the bios from starting.