Can you reset your device by holding the power button and home button down simultaneously until you see the Apple boot logo?
If that doesn't help, plug it into iTunes, and try holding the power and home button for 10 seconds, then release. After you release, just press power once.
If that doesn't work, try this combo:
- Hold down the Sleep/Wake for 5 seconds (do not release it after those)
- Keep holding Sleep/Wake and press the Home button for 10 seconds
- Release the Sleep/Wake button but keep Home pressed until the Apple Logo appears (or after about 30 seconds)