Xbox controller

Try re-syncing the second (non-working) controller to the console. To do this turn both the controller and the 360 on, then find the little sync button on the 360 controller and hold it down until the lights flash in a clockwise circle. Now find the sync button on the 360 console and hold it down until the lights on the console spin in a clockwise fashion. Wait a couple seconds until the two sync up and then voila, you're good to go!

Here's pics of what the sync buttons look like: