Have a core2duo based system, suddenly stopped booting up at all, suspected PSU and replaced it, still wouldn't boot. Tried 'faulty' PSU in a working PC and it booted fine. Assumed it was the motherboard, so replaced the core2duo motherboard with a AM2 one, put everything together and it booted before I had time to boot from my windows CD to format it. I restarted the computer and now the fans just spin and lights come on but can't see anything on the monitor.