Sounds like a corrupt floppy disk to me. It might be best to work on a copy of the disk so that if something goes wrong you have got the original to go back to. I would use DISKCOPY to make a copy of the disk to play with.
I have used a programme called "File Rescue Plus" in the past under MS-Dos, but it doesn't run under Windows. Do you have access to a Windows 95 or 98 machine that you can run as a DOS machine, i.e. stop Windows loading, which has a floppy disk drive, so that you could try out a programme like "File Rescue Plus"?
Perhaps someone else will know of a similar programme which will run under Windows.