Originally posted by: Hal 9000
This happens for a few various 'home-made' discs.

Did you burn them in the same drive? Or were they burned in a different drive ?

If they're discs you burned, could read before, but can't read any longer, then it's possible the dye is fading as adywan suggested.
If you got them from somebody else or burned them yourself in a different drive, then it's possible the dye is still good but your current drive just doesn't like that particular dye flavor.
Unfortunately some drives don't get along with some dyes, even when the dye is new.
Definitely try reading them in as many different drives as you can beg, borrow, or steal.