If one app isn't responding
If you see a black screen
You should see a battery icon while your device is charging. If you continue to see a black screen, reset your device.
If your device doesn't respond when you press buttons
Your device might not return to the Home screen when you press the Home button, wake from sleep when you press the Sleep/Wake button, slide to unlock or power off, or it might appear frozen. Try these steps:
If your device gets stuck during startup
When starting up, you might see the Apple logo or a red or blue screen for a long time, or your device might restart again. Try these steps:
Get more help
If you still need help after trying the steps above, contact Apple Support.