Blu Ray Discs stopped playing correctly

[tgor1]

I have several blu ray discs that have stopped playing correctly within the past year (including Casablanca, Singin in the Rain, Annie Hall, When Harry Met Sally, etc.). The discs don't appear to be scratched, and all have played fine in the past. They will each play part of the film and then freeze. Sometimes they will skip ahead missing most of the movie. The same problem happens on different players, so it's not a player issue.

1. Is there a way to fix these discs?
2. Is there a way to prevent this problem from happening to the rest of my collection?