•My screen is on, but it doesn't respond when I tap, slide, or try other gestures. Why?

Try to force it to restart

Restartt

Hold down the sleep and home keys for about 20 seconds. When you see the silver apple, let go and let it reboot. No data will be lost.

Force close an app

Follow the tips at this link If your iPhone, iPad, or iPod touch doesn't respond or doesn't turn on - Apple Support and make a Genius Bar appointment if the issue persists.