Computer won't POST and powers up on its own

[TheBronze]

I shut down my computer and when i wanted to start it again after a couple hours later it wouldn't POST and only gave me a black screen. If i turned off the PSU switch on the back and turned it back on again no matter how many hours has passed it would power on its own, but if shut down my computer using the power button and did the same thing it wouldn't do it.

 

Things i have tried:

Everything in this sticky except the ones that require a motherboard speaker because i don't have one.

Cleaning off all of my components because i've read that dust could cause shorts

 

Switching monitor power cable and PSU power cable in case it was broken

 

Buying a new CMOS battery

 

Taking off case cables to see if one of them caused shorts.(it still did power on its own)

 

My specs are:

CPU:Amd Athlon x2 5200+
Motherboard:Asrock N68c-GS-FX(Latest Bios)
Ram:2GB 800 Mhz DDR2 Kingston ram
GPU:Radeon HD 5570
PSU:Xigmatek NRP PC502 500+ Bronze