I just replaced my Gigabyte GA-P55-UD4P motherboard with a GA-P55A-UD3. My 4GB of G. Skill DDR3 RAM is only being half used. Windows 7 64-bit says "4GB (2GB usable)", and the resource monitor shows 2GB are reserved for hardware. My bios say one stick is not enabled. I can't find any options to enable it. My gameplay has shown that there probably is only 2GB being used. Does anyone know why this is?