DO THIS AT YOUR OWN RISK!!!! BACK UP ALL FILES BEFORE PROCEEDING!!!

To defrag ALL of your hdd open regedit...
go to HKEY_LOCAL_MACHINE/software/windows/current version/applets/check drive/defrag/appstart params
back-up the exclude files string onto a floppy then edit the registry deleting all information in exclude files.
restart then defrag in minimal or safe mode (depending your version of windows) after defrag then deceide whether or not to restore the registry.