I just bought D.G. for the XBOX 360 yesterday. It was awesome until today. I was on the sixth mission when I tried to go back to the previous checkpoint and it just restarted the level. I was on the 14th wave of 15. So I played it again, got overwhelmed, and the same thing happened. Then it got worse.

Now whenever I play ANY level pressing the "back" button once restarts the level, and it seems to randomly end with "Defeat" in the middle of play, but still gives me a bronze medal AND i noticed that the words "Cheat mode on" appear in yellow on the screen once in awhile. I DON'T want any cheats, and don't know any, and may have inadvertantly activated one (? this is the xbox not a PC). Please help.