I'll keep this short and simple cuz i'm at work. When i turn on my comp all the fans and leds light up, but it doesnt make that "beep" sound and boot up. My brother took it apart (he built the thing) and told me the motherboard cpu and HD are all fine from what he can tell.
---------- Post added 2011-10-05 at 03:16 PM ----------
And maybe u can change your RAM to a different slot, might help ( helped me sometimes ).
If u got a 2 PC's , u can try and switch some parts to test if they really work, like CPU, GPU, RAM, motherboard.