First, I'd recomend looking at the disc for any damge, depending on the damage, the disc (or at least parts of it) may be unreadable or present faults when read (such as music not playing/presenting faults at points). Second, find someone who has the proper tools and method for cleaning the disc, I don't know any names in English, but there's a kind of paste and that's realy good when used with certain disc spinners to do this job, if the person doing this is good, the disc will be good as new and will work perfectly. Or you can try doing it yourself with whatever tools you have at your disposal that's good for cleaning discs, but that may not work depending on the problem as well as you'd have to shoulder the risk for damaging the media if done improperly. Either way, I hope the besto for you! Good luck with your disc!