I had a strange issue, the computer refused to post twice leading only to a black screen, the third time it booted but I noticed windows was reporting my memory as 8GB (3.97 GB usable) and that i was in single chanel. All my settings should be fine the only thing I changed that day was that I fetched all my updates at the same time. When I assembled this system the memory worked fine and in dual channel. I'm using windows 7 ultimate 64bit, an asrock 970 extreme3, 2X4GB gskill ripjaws the phenom 2 X4 975 black edition CPU and an XFX Radeon 7950 3GB black edtion.
ram pn: f3-12800cl9s-4gbrl