I built a heck of a lot of machines with the M7NCD Pro, but only a few with the M7NCG (too many problems with the onboard video enabled). Some tips dredged from the deepest crevices of my memory (so take with a grain of salt):
This board can be picky with RAM. Some BIOS releases are better than others in this aspect. Google for an enthusiast webpage somewhere to find the better BIOS versions for you.
Running the sticks in single channel mode can sometimes be the only way to get the board bootable/stable. Some cheapo memory (Elixir 512MB sticks come to mind) can be used only one at a time, and then a small bump in VDIMM is required for stability. Try a single 1 GB DIMM at first and see if you can get the board to POST and recognize all 1024 MB.
I recall running into problems with the IGP at higher resolutions (1280x1024 and above). If you have an AGP video card to hand, disable the onboard graphics and use the discrete video card. For some reason some of the M7NCG boards I had didn’t like to run the memory at 200Mhz or even 166Mhz with the onboard graphics enabled.
All these pointers are fine and good, but I guess your problem lies more with recognizing all your RAM than getting your system running smoothly. Try updating the BIOS to the latest version and installing only one of your GB sticks. If you can get that working, add the other stick. Putting both sticks into the slots that are right next to each other might work when having them in dual channel configuration doesn’t.
Honestly, you might not be able to get these sticks to play nice with your board. Try to come to a decision before the easy-return period on your memory purchase ends.