Some games do that. I've gone through about three copies of Quake III that simply refused to boot - all neat and clean and shiny. Apparently Sega acnowledged that there had been a batch of duff GD-ROM discs early in the system's life, that you could send back for a free replacement (that EGM apparently ran a full two-page spread on, then go on to ignore the PS2's rampant DRE problem aaaaargh). All you can really do is ... uh, buy another copy. :/