Do the parking/running lights work? Starting with the easiest, I would use a voltmeter to make sure the bulb is good (use the continuity setting), then see if there is power getting to the wire using a volt meter. It's possible a wire got pinched, has a bad connection, or got severed somewhere between point A and B. Good luck!
Have you tried plugging it into the computer to see if it registers? If it gives you an error, maybe google the error to see the meaning. Just a thought
Try the easiest first....try cleaning out the dock connector with some canned air to see if there's anything keeping a good connection from being made. If that doesn't work, open it up and see if anything has come loose/broken etc.