Rebooting your phone is an easy way to solve issues you might be experiencing with the device.
To reboot your phone, press and hold the power button and the volume up button until the screen turns off.
Your phone will automatically reboot.
If you are prompted to, enter the PIN code of your device.
Drag up on your device to unlock it once the reboot has been complete.
If the problem persists, you might want to try doing a ‘factory reset’ to solve the problem. With a factory reset, the device is reset to its original factory settings.
Note: In contrast to a soft reset, with a factory reset all of your apps, settings and data – including contacts and photos – on the device will be deleted.