Additional memory installed not showing in system

I have a Gateway GM5442 with 2 1024 MB DIMMs memory originally installed and just upgraded it with two additional DDR2 PC2-4200 1 GB Samsung memory cards. The computer works as before, but the additional memory does not show in system. I use Windows 7 with 64-bit OS. I already checked that the cards are quite in place and rebooted. I already checked as per your instructions msconfig Advance...