I agree with Ted. A complete re-installation would be best, preceded by a format. Quite often it's faster to re-install it all, instead of using hours and hours and hours trying to fix the problem... and in the end, you may still have the root of the problem left in your system, just to pop up at some moment.
I stress one thing: have your Windows on a separate partition, perhaps with some necessary programs, BUT DO have your personal important files on another partition, or preferably another disk. That way a total remake of Windows won't eat your valuable files.