Try going to:
tools/folder options/view then untick "hide protected operating system files" and press aplly and press ok.
See if there are any massive files that were hidden.
Chances are its restore ...go turn system restore off completely (this is your choice to do) & that should clear out the restore points & free a LOT of space. Free to turn it back on again and create a new restore point (but personally I wouldnt bother with the windows system restore at all. Get yourself a good stand alone backup program *wink*)
Hope that helps somewhat
