X-box 360 Halo Players

[Rumika]

I finished COD4 during the christmas holidays and am working on Gears of War, I am at a point where I have to kill everyone to go onto the next stage but I keep getting taken out. I did find some cheats but they do not seem to work with the 360, some are talking about the white and black buttons.
I am at the start of Into the belly of the beast and I am playing legendary player level.