Why won't an Xbox 360 play a new Xbox 360 game?

if its an xbox360 its because it is only slightly cross compatible and it can only play somr of the games and if its the original its probly cause the disc is scratched and to fix that go to gamecrazy or GameStop and ask them to buff the disc which will make fillings into the disc itself... most scratches you see on a disc are just scratches onto the gloss on the outside of the disc...if the scratch is severe it will make some damage to the encoding and writting on the disc itself...but luckily buffer exists and it will fix a great amount of dangerously deep scrathes