Format C :-))))
If you re-install it will take you back to the original state. You should have a recovery disk which will have all the drivers on. If you have, use that. If not, make sure that you have all the relevant driver disks. The whole operation should take an hour or so.
You could delete all the temp and cookie files. Gl to start-control panel-folder options and ensure 'show all folders' is ticked. Then go to My Computer-C-documents and settings. Click on each name and delete everything in the cookie files and then, in each user, go to 'local settings' and zap all the files in temp, temp internet and history. You could also download the free version of Adaware from click here and run that. Delete all programmes that are not used in the add/remove section of control panel. A trip to the defrag button, reboot and see if it runs OK.