SCANDISK FAT ERRORS

I have a laptop running Windows 98 which hangs when I run Scandisk for Windows.
When I boot up in DOS mode and run Scandisk it stops with the error message “Scandisk encountered a data error while reading the FAT on drive C – this error prevents scandisk from fixing the drive”
Is there any way of forcing Scandisk to fix the FAT error or any freeware tools to to do this?
The obvious alternative is a complete reformat of the drive and re-installation but time consuming!!