XP product activation after reformatting

I had a virus and reformatted my system and reinstalled Win XP(original disks that came with the system). It never asked me for a product id # when installing, but appears to work fine except for two things: It will not let me install any microsoft product even with the id codes (says that they are invalid)and when I attempted to figure the problem out on microsofts website it shuts my computer down. I repeat that these are original disks that came with my computer.. not some pirated stuff. Any ideas on how to solve this???