Do you have this problem only with a single specific disc or with every disc you try? If this issue is with only a single disc, the most probable cause is a scratched or dirty disc. Cleaning the disc can improve readability, but a too large scratch often make a disc totally unreadable. Try to read that specific disc with a different drive (maybe you can ask a friend if you have only one drive).
Do you have problems with burned discs only or both with burned and pressed discs? If the problem is only with burned discs, again the most probable cause is the support, i.e. you are using low quality media, that after some time become unreadable. Again, you can try to use a different drive to recover data (different drives have different capabilities to read damaged discs).