PC freezes every time

[Ace king]

Recently I built a new computer with this specs:

Intel core i5 750
ocz gold edition
GA-P55A-UD3R
and ati 4670

the problem is making me crazy because I don't know where is the problem

the computer just freezes at any random time(also the mouse and keyboard freezes) and I have to press restart button

the computer freezes if left alone or if left in bios(what I think it's hardware problem)
also after minutes of playing games

I tried to:
1-making check for gpu and it's ok
2-changing the slot of ram

I waited so long to build the computer and now I can't work on it!

Thanks in advance

 

[fastco]

What power supply did you use? Wattage, brand...Check all your connections and run Memtest on each stick of ram for at least 7 passes.

 

[JMMD]

Have you tried testing the ram to be sure it's good? Try memtest or something similar.

How are the temperatures?

 

[veldom]

I could well be a power issue, check your power supply can handle the demand.

I had a similar issue with a friends i7 that he'd built and it kept crashing and rebooting itself. Turned out it was overheating and he hadn't locked the heatsink over the cpu properly so it wasn't forming a good seal and thusly not cooling the cpu down enough.

 

[Archean]

Check your system's Event Viewer Logs to see whether something of useful nature can be found there to troubleshoot this issue.