if there is a virus on the hard drive then formatting the drive will erase the virus anyway. occasionally, corrupt sectors can prevent a successful format if you are using 3rd party software such as partition magic. if this is the case then you should, as j2buttonsw suggested, do a low level format (also known as writing zero's to the drive). this takes a long time but completely blanks the drive without fail (unless you have dropped it one to many times causing internal damage). go to the drive manufacturers website to download a low level format program. if you have already tried and failed at this hjen there is internal damage to the drive, not caused by a virus.