Hi reikal,
I can't tell for sure what the problem is, but try looking in the BIOS to see how much ram it see's.
I'll be able to help you further if I know what the BIOS shows up in RAM.
I suppose you know how to boot into the BIOS? If not, reboot your PC, and when you see something appear on your screen, you'll see something like "Press F2 for settings". Press the key that is said as soon as possible before the Windows boot, and you'll be in the BIOS.
Then just navigate the tabs and you'll see the computer infos in one of them.
Cheers,
Fire Cat