Halo 3 Single Player Problem

I just got my 360 back from MS(3 red lights). I have had no problems with it so far, but when I tried to continue my Halo 3 single player game, it shows the loading screen, then goes black, then goes back to the main menu instead of loading my game. Also, if I try to just go to campaign, and start from the mission i was at, it starts to load, then kicks me back out to the campaign lobby saying that the game was cancelled because one of the players has left. Anyone know what to do?

Thanks.