When your computer starts running slow and is cluttered with programs, it is time to reformat your hard drive. Reformatting deletes everything from your hard drive. Basically, you wipe everything out of your computer after you back up files on to a disc. After cleaning the hard drive you load your operating system and files back onto your computer. For more details on how to delete everything
. from your hard drive check out this site http://www.ehow.com/how_4478239_delete-everything-hard-drive.html.