go through the pages on this site, there are many powerful tools to help with this.
http://www.bleepingcomputer.com/download/windows/
but as others said, format and reinstall.
actually, format, install a Linux distro(use all diskspace), low level format (write zeros to drive), reinstall windows. some sneaky ones can hide from a windows to windows format
http://www.bleepingcomputer.com/download/windows/
but as others said, format and reinstall.
actually, format, install a Linux distro(use all diskspace), low level format (write zeros to drive), reinstall windows. some sneaky ones can hide from a windows to windows format