A restart (soft reset) can resolve issues like continuous resetting/rebooting, device crashing, freezing, device locks up, and keypad doesn't respond.
A soft reset (turning the device off then back on) is similar to restarting a desktop computer and is one of the first steps in troubleshooting a device. A soft reset won't affect data on the device.
Press and hold the Power button until "slide to power off" appears then release.
For devices without a Home button, press and hold the Power Button and the Volume Down button until 'slide to power off' appears then release.
Alternative Method: Settings > General > Shut Down.
Slide the Power switch right.
Allow several seconds for the device to power off.
With the device powered off, press and hold the Power button until the Apple logo appears then release.
If the device doesn't respond to input or restart, press and hold the Power and Home buttons until the Apple logo appears (approximately 10 seconds) then release.