One site said you should not run chkdsk on the drive as it may damage it and write over data but that doesn't make too much sence unless its doing changes to the drive.
Anyway I mite try SpinRite.
Currently im running a scan with a program called Recover My Files, 10 hours in and its done 6,173,263 of 240,121,729 sectors. Its going really slow at some parts and taking ages to get to the next sector so there may be damage to it.
I should of picked a newer drive for my backups.