Try a Reset...
Reset ( No Data will be Lost )
Press and hold the Sleep/Wake button and the Home button at the same time for at least ten seconds, until the Apple logo appears. Release the Buttons.
If no joy...
Connect to iTunes on the computer you usually Sync with and Restore
Make sure you have the Latest Version of iTunes (v11) Installed on your computer
- iTunes free download from www.itunes.com/download