A soft reset can resolve issues like continuous resetting/rebooting, device crashing, freezing, won't ring or vibrate, 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. In most cases, a soft reset won't affect data on the device unless the battery is very low.
If the device is unresponsive or won't power on, press and hold only the Power button (located on the upper-right edge) for 20 seconds then release. Then press the Power button again for 2-3 seconds until the device restarts.
If the Power button method doesn't work, charge the device for a minimum of 4 hours using the supplied charger or 12 hours if using a different charger.
Press and hold the Power button (located on the upper-right edge).