PC freezes in dual-channel mode

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.

System if it helps:

MS Win 7 64-bit

Athlon II x3, unlocked to an Quad

MSI 740GM-P25 Mobo

2GB DDR3-1333

HD 5770

WD Caviar Blue

600W OCz Stealthstream PSU.

Thank you!