A soft reset can resolve issues like continuous resetting/rebooting, device crashing, freezing, won't ring or vibrate, can't make or receive calls, 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 won't power on, press and hold the Power, Volume Up and Volume Down buttons for 1-2 minutes.
Press and hold the Power button (located on the top edge of the device).
Drag the window to the bottom of the display to power off the device. Once the 'goodbye' message appears, allow up to 15 seconds for the device to completely power off.
Press and hold the Power button to power on the device.
If unable to power cycle, perform a soft reset. Press and hold the Volume down (located on the right side of the device) and Power button simultaneously until phone vibrates, then release both keys.