defragging the HDD does find errors, to fix those you have to use scandisk. If there are errors scandisk will allow you a couple of options, reclaim the space by deleting the lost clusters/files, or try to recover them. Defraaging will not do this, when defragging if it finds an error it normally kicks you out and says to run scandisk. Had nortons stuff once caused so many problems I binned it as many others have done.