The original xbox's crystal wears out over time. Eventually it will just stop reading games. Later released versions and the xbox 360 don't have this problem, but if you got it within a year or two of release, this is probably the reason for its failure. The only solution is to replace the disc drive since i'm sure the warranty has expired. It could be a different problem, but this one is common if you're getting an orange light or a disc-unreadable error.