I'd also check to see if there is a BIOS update available. If you're in EZ mode bios view, you'll want to switch to Advanced, and save the setting for the advanced view being default from now on. There should be a setting in there to do that as well.
Pressing F7 will switch you from advanced to EZ and back, if you prefer.
If you have overclocked the CPU at all, I'd return it to standard settings until you resolve the DRAM issue. Might not be a bad idea to simply reset to optimal default settings as a place to start, if you haven't done that already. Pressing F6 while in the BIOS will load the optimal defaults.
You can also try installing both modules with the power disconnected from the back of the PSU, removing the CMOS battery for a minute or five, reinstalling the cmos battery, plugging the power cable back in and rebooting. Probably won't be the fix, but I've seen it work by resetting the hardware tables before.