PC NO DISPLAY BUT HAVE POWER

got a problem on my pc. when i opened it i heard a long beeping sound. then i checked the VGA and the memory if they are still in place (and they are!) then i removed my processor… i tried to used thermal paste but still hear the beeping sound. then i decided to remove my processor and put it in a box for a week. after a week…i put it back again. when i turn on my pc there’s no beeping sound but there was no display on my monitor. i already checked all the cables and parts and they are in good place. and then i tried to recharge my Ipod Nano on my USB port and it’s working! my Ipod battery got full anmd working. i dont know what to do… can u help me on this? thanks in advance!