New Built Computer Problems

[Tostiganator]

Hey, so I just recently build a new computer with these parts:
i5-3570k
Sapphire Radeon HD 7870
Gigabyte GA-H77-DS3H
Seasonic 620W PSU
Samsung Spinpoint 1TB
G.SKILL Ripjaws 8gb

I put it together and it loaded up great, runs great, but has one problem that keeps popping up. Often times while I'm playing some game, my monitor will lose input from my computer and the computer crashes. But when it crashes, the computer's power button light is still on saying the computer is on, but the hard drive activity light is just blank all the time. Also the sound makes that buzzzzz noise that happens when computers crash. It seems happens at random intervals of time.
I've checked the inside over and over and I see no problems with all my connections. I thought it could possibly be a problem with the hard drive losing power so I switched out the power cord for the hard drive for a spare I had but still had the same issue. I do not have too much experience with computers so at this point I'm stuck as to what to do.

Any help or suggestions of what may be wrong is greatly appreciated!

 

[o1die]

Sounds more like the power supply; sometimes the caps on them make noise. You may also have a driver or power issue with the video card.

 

[Tostiganator]

Sounds more like the power supply; sometimes the caps on them make noise. You may also have a driver or power issue with the video card.

I should have been more clear, the sound was from speakers not from inside the case.