If your computer is running really slow and youve tired to fix it and given up and started to do crazy things and then totally screwed your computer, the best way out of it is to wipe your hd and reinstall windows.
This happened to me a month ago, it was hard but i mangeded to get my computer back the way it was in about a week.
If you have vital things on your comp and you dont want stuff lost, what you can do is the the windows OS cd and reinstall windows but dont wipe you hd this will repair all the stuff in the system32 folders.
p.s. there is no harm in a little xxx mate