Originally Posted by Lexluethar
Two things come to mind. First is your motherboard may not support 4 gig of memory - check the manf website to see what it can support. Second is if this is a 32 bit architecture it is only going to recognize 3.5 gig INCLUDING your video card.
But BIOS would recognize all 4GB (I know mine does). OP said that BIOS only recognized 2GB of the 4GB, so its not a Windows (or architecture issue).