hmmm... there are alot of solutions for this matter. try to defrag your hard disk, and all initial parts of it like if it is devided to more than one partial. C, D,E..etc.
Then I suggest you search for any parts of the prgrams that you uninstalled before. if you can have windows washer it'll really help getting back the lost space. it is a really tiny program that washs all the cookies, all the left over of programs and such.
also, i suggest that if you have more than one partial of the hard disk that you save all your documents and stuff in the other partials, like D, E...etc. and not in my documents as the last also is part of the partial C.