I am using Windows 10 Pro 64 Bit. I have installed 2x2 DDR3 RAM modules of same model, same frequency (1333 MHz), same voltage to my motherboard. But the PC shows that only 3 GB of it is installed and 1.75 GB of it is usable. I have tried to configure the settings in msconfig and updated my BIOS in the motherboard, but still it shows the same. However, when I use a single RAM kit in either of the slots, it shows OK (2 GB shown, 1.60 GB usable). Where is the problem then? Please help. My motherboard is Gigabyte GA-78LMT-S2PT (Rev. 4.2).