You mean you have a boot sector virus on your hard drive? (as opposed to a floppy)
Try another AV - eg, one of the free ones, AVG or Avast.
Or you could try writing a new mbr (either run fixmbr from recovery console or boot from 98 boot floppy and run fdisk /mbr (make sure floppy is write protected). This fixes 95% of boot sector viruses (there is at least one where this won't work - in fact probably leave your system unbootable - so check Norton's AV database to see what it says).
Boot sector viruses are not common nowadays (as floppies are rarely used to transfer data any more).