You cannot format your c:\ the one with the operating system on from within windows.
Formatting will delete all software in this partition.
The only way to format c:\ is to boot from floppy or CD format the c:\drive and re install windows. Then re install all your software and drivers.
Clean install windows 98
Clean install windows XP
Try cleaning the registry first and then make sure you have decent antispyware install and upto date these are all free.
Registry cleaner :-
Regseeker click here
TweakNow RegCleaner 1.3.2 click here
Easycleaner click here ( Use with care, It advises you to back up the registry first, this is a good idea as it cleans rather aggressively. )
Anti Spyware :-
Adaware click here
Spybot S&D click here
Spywareblaster click here
a2 click here