Help, My computer won't come out of sleep mode.

Hey, I recently bought a custom built gaming rig and I am very satisfied with it. However I have noticed a problem lately. Whenever I leave my pc too long inactive it'll go into sleeping mode but won't come out of it anymore. The pc actually freezes, as the caps lock lights won't lit and the pc is unresponive but I still hear the fans running. I have to reset the machine manually so it'll work again and it annoys the hell out of me. I just joined this forum so I might find a way to fix this problem. I am suspecting that either my PSU is to weak or that my pc overheats but I think it's the PSU. Here are my specs:

OS: Windows 7 Professional 64 bit
MOBO: Asus 990FX Sabertooth
CPU: AMD FX-8120 Bulldozer 3.8 ghz
GPU: GTX 560 Ti Coolstream 2048MB Vram
RAM: Corsair Vengeance 2x4GB
HDD: Seagate Barracuda 2TB
PSU: OCZ 500 watt
(I'm also thinking to buy an SSD for my OS)

Like I said I am mainly suspecting that my PSU is to weak but I'm not sure that's why I'm asking here. I hope to find a solution soon

(Sorry if there are some grammar errors, English isn't my first language)

To the Overclockers forums

Do you have Hibernation enabled? Or did you ever disable hibernation?

It's enabled I think, the monitor goes black but I can't get it to it's normal state again. I have to manually reset the pc.

Some PC's don't do well on hibernation etc. Let the HD spin down and the monitors turn off, but don't let the PC go into full sleep mode.

Click start, right click command prompt> Run as administrator>Type powercfg-h off>exit

Try this and see if it freezes next time the computer goes into sleep mode.

Ok thanks I have done that and I'll see what happens.

I had the same problem till I disabled hibernation.
Might be a Sabertooth issue

Ok that worked, so far my pc hasn't frozen yet and I have kept it inactive for 4 hours. So yeah thanks, I guess it wasn't the PSU after all