like totally reformat?
That means you lose everything, so make sure you save everything onto discs before you decide to reformat. You should have recovery discs that came with ur computer, so once you've saved what you need to save, just insert those discs and you can start reformatting with those discs. Some computers now dont come with those discs anymore....I told me if you press the number 0 while the computer is starting up, that should work the same