Computer freezing periodically during games

While playing LoL and Magicka my computer has been freezing and while this occurs, no error message pops up and the mouse disappears. It started out doing it every few hours or so, and is starting to happen a little more frequently. It unfreezes after a minute or so and everything is fine. I just built the computer a couple days ago so I'm worried I may have messed something up. Thanks for taking a look!

Operating System: Windows 7 Professional 64-bit Processor: Intel(R) Core(TM) i5-2500K CPU @ 3.30GHz (4 CPUs), ~3.3GHz RAM: CORSAIR Vengeance 8GB (2 x 4GB) Card name: AMD Radeon HD 7850 Motherboard: ASROCK Z68 Extreme3 gen3 HDD: SAMSUNG Spinpoint F3 HD103SJ 1TB 7200 RPM SATA PSU: OCZ ModXStream Pro 600W Modular High Performance Power Supply