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 (powering 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.
Press and hold the Power button (located on the right side of the phone below the volume button).
Once the "slide down to power off" message appears, swipe down then allow several seconds for the device to power off.
If unable to perform a soft reset, remove then re-insert the battery.
If necessary, press and hold the Power button to power on the device.