I am having the exact same problem that you are my friend. Both ram sticks work alone in both dimm slots. I thought at one point that it may have been a power supply problem but I just recently changed power supplies and the same problem still remains. I'm wondering if it has something to do with my bios settings. I can't seem to find any help on the subject. One that is odd about this whole thing is that when I first had recieved my sticks and installed, they both worked. It displayed just of gig of memory now it just will display the 512. Any help would be appreciated. Oh and I do have the latest bios 1.1b.