Sounds like the DVD lens inside may either be dirty or out of alignment. You can first try using a DVd lens cleaning kit to ee if that fixes anything. If not you will have to look into getting that lens lined up again. Doing this requires taking the system apart somewhat so i only recommend doing this if you are absolutely sure of what you are doing. A Google search for "PS2 lens alignment" should bring up a number of pages on how this is done.