That sounds major like, I recommend using windows restore and go back to a restore point a few weeks/months ago, however long you think is necessary.
If that fails to work, get your trusty XP/Vista disc out and try to do a system repair, if all else fails I would recommend a clean install of windows...
But before you do ANYTHING, back up all your most important data and files
, either to a different partition or if you have an external HDD, use that
Good luck, let us know how it goes!