I am having problems with my new operating system

My computer is on Vista and the problem that I’m having is that it freezes every few minutes regardless of the activity on the computer. I have asked Dell for support and they had me restore it, told me it would be fine. Here are the specs: Dell Dimension 9200, Intel Core 2 CPU 2.4Ghz, 2 Gigs RAM, 256MB Ge force 7900GS
