My Xbox 360 won't play GTA IV. All other games and DVDs work. What can I do?

My brother bought the game and when he tried to play it it got stuck at a screen asking him to sign in. There were two choices "yes" and "no" but the ons on the controller didn't work. I unplugged the rock band instruments he also had plugged in and the game started fine. There was some interference, but it's hard to say who's fault it is. So if GTA IV doesn't work but other games do, make sure you don't have the rock band instruments plugged in.