Have you tried a Reset...
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... Try a Restore...
Connect the device to your computer and open iTunes.
If the device appears in iTunes, select and click Restore on the Summary pane.
If the device doesn't appear in iTunes, try using the steps in this article to force the device into recovery mode.