Computer Completely Freezing

I bought mostly all new parts for a computer and put them together. It all seems to work just fine other than; after about an hour or so it completely freezes up. The only solution is to restart. Upon restarting it /sometimes/ freezes as soon as I log in and rarely beforehand, if I leave it for a while it'll last longer. I assume it's a heating issue, but there doesn't seem to be any excess of heat, nor does there seem to be any fluctuations indicated by any monitoring programs.

-ASUS Radeon R9 280X DirectCUII TOP 3GB
-ASUS Sabertooth 990FX Motherboard R2.0
-AMD FX-9590 8 Core Black Edition Processor
-Vantec ion 2 600watt power supply
-2x corsair CMx4GX3M2A1 4GB DDR3 RAM

OS: Windows 7 Ultimate x64