Boot with the single memory and go into bios and put the memory voltage at 2.6v or +0.1v, which ever option there is (i think the default is 2.5v?). Also update your bios, it could improve memory issues, but do it before you add the voltage. If that doesn't work... I don't know :P
oh! If there is AUTO settings in the bios for ram timings use that or add 1 to all the timings eg. Cas 3 -> 4.