Halo 3 maps not loading?

[blackend_rines]

I'm trying to play halo3 and none of the original maps will load. I can't play anything at all not even story mode. My little brother put in a cheat code the other day, could that have screwed it up, or is it the xbox itself, we bought it used. The cd is clean and barely any scratches are on it. If anyone knows what has happened and how to fix it please tell me. Thanks.
The scratches are very light, I doubt they're the cause of the problem.

 

[David S]

if any of the scratches are deep it will not be able to read it. That happened to me to. best way to fix it is to buy a new disk