That's a classic sign of the data on your floppy disks having become corrupt, I'm afraid - it happens a great deal. Unfortunately, many people - myself included - thought that information stored on magnetic media would last forever. But, in many cases, it didn't. I'm not sure there's anything you can do - but someone may come along with some ideas.
Sniper Elite 4 review: Headshotting Nazis has never felt so good