Okay so I built me a PC back in December and I had problems with random hard freezes, which I first suspected the CPU, so I called up AMD to request an RMA but they said check the GPU, and other components before requesting an RMA. So I updated the GPU drivers and set my CPU to stock, and then I went on browsing, yet it still locked up on me.
So to cut to the chase, I decided to check out the memory, so I took out one of the two (Kingston Hyper-X 2GB DDR3-1333) sticks and well I had no problems. I went several weeks with no lock ups with only 2GB installed in a single slot, but I decided I wanted to go back to 4GB for gaming. To test the sticks I decided to switch out the two sticks and still I had no problems. Its only when there is both 2gig sticks installed when I have issues.
Maybe low voltage on the ram or timings and/or command rate to tight! I would start out checking the voltage. This I got from Kingston Site;
"1.7v - 1.95v voltage range for dual-channel applications for AMD based systems and Intel chipsets older than X58
1.65v voltage for triple-channel Intel Core i7 9xx series applications
1.65v voltage for dual-channel Intel Core i5 7xx series and Core i7 8xx series applications" http://www.kingston.com/hyperx/products/khx_ddr3.asp