Does the ram upgrade show up in other OSes, such as windows or other linux distro?
What kind of computer do you have also?
As far as this being a MINT only problem I really wouldn't know, I just started using Linux a few weeks ago.
Custom-Built comp, Mint for desktop, Windows Vista for gaming, shared data partition for personal docs:
AMD x2 4200 2.2ghz
MSI 8600GTS stock OCed
Asus m2n-e mobo
2x1gb, 2x512mb=3gbs ddr2 800
Seagate 230gb drive