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for some reason whenever i try to start black ops on my ps3 now (orig disk) i just get a black screen

i tried the disk on a mates ps3 and the multiplayer loaded up (but did take slightly longer than it should of done normally but eventually loaded).
any ideas why it wont play at all on my ps3?
btw i delete all the black ops game data and that didnt help :/
the game used to work fine, and the next time i tried playing black ops i just get a black screen.
help please?