Halo3 and game freezes GTA IV as well

Try using a DVD cleaning disk, It's odd that it would have a dirty lens if it is somewhat new still. Also, try seeing if it freezes when you turn the xbox on (with game inside) by using the main button on the console. For some reason certain games will freeze randomly if you turn your system on with the controller (I'm not sure why yet)

If that doesn't work, you will most likely need to contact microsoft, a new game should not stall a new xbox. Your xbox should be under warranty for internal issues ( Don't open it yourself )