Compact persario hp desktop MB problems

I recently had my computer serviced by a friend of a freind who assured me he knew what he was doing because it was his job. I had locked the system up so bad it would not unlock even after rebooting and other things. It just would come on and freeze on the windows meadows opening scene. Well when he returned the tower the sysem was working but it would not accept my windows office 2007, or my print artist and several applications that should have been there aren't and the restore disc won't work either. When I brought this to his attention he stated that he could increase the memory stick but it would cost extra which I declined, so I looked in the system info and it says 512MB which is what it is supposed to say but the system properties it say 384MB can you tell me what has happened and it this preventing me from restoring my much needed programs and how can this be fixed I depend on my computer fo my home & business needs