If you wish to reformat your hard drive and there is only one as in your laptop . I would download on to a usb stick a program called Active Kill Disk put it in your computer and let it do its thing. Another way would be to remove the harddrive and attach it to another computer via a usb adapter and use the Windows program on the remote computer to do it and once done reinstall it in your laptop and then do the clean install . I am assuming that your previous OS was XP
galeck1947