i recently left my computer on while i was at work and when i returned it had shut down, thinking that it had just gone to sleep i pressed the power button and it came back on, that is all the hardware, monitor, hard drive, video card, fans, and led's came on. but it didn't beep signaling the start up. does anyone know why this would happen? all my components have power and the computer worked 2 days ago just fine. if anyone has any ideas please let me know. thanks.