try moving all your save/download content onto a flash drive then remove it from xbox start a new game then when u get started pause plug flash drive back in then select load game should work this pretty much bypasses login at start also a way to steal dlc for other games i.e. signing off xbox live and copying a friends dlc or downloading it off the internet and using a mod program to inject it into ur xbox360 flashdrive
Try disconnecting the xBox itself from the Network/Internet completely when loading the game.
If it still hangs at that point you may have a dirty spot or scratch on the disc near the center(the autentication of authenticity area). I ran into that same problem and it was cleared up after taking the disc to a local video rental store and paying them to do a scratch repair ($4 depending on the store)
