Perform a soft, factory, and alternate master reset of the device.
INSTRUCTIONS & INFO
POWER CYCLE YOUR DEVICE: There are multiple ways to reset your device if you are experiencing issues. The first step is to power cycle your device. Press and hold the Power/Lock button, then select Power off. To turn the device back on, press and hold the Power/Lock button until the screen lights up. Note: If you are unable to power your device off or if it becomes unresponsive, press and hold the Power/Lock button for 10 seconds, until it reboots.
RESTART YOUR DEVICE: Press and hold the Power/Lock button, then select Restart.
FACTORY DATA RESET: If you are still having issues with your device, you may need to do a Factory data reset (Master reset). This will erase all data on your device and restore it to factory settings. Swipe down from the Notification bar, then select the Settings icon > Backup & reset > Reset phone > RESET PHONE > OK. Note: A Factory data reset will revert the device back to factory settings. It will permanently erase all personal data, preferences, settings and content such as pictures, ringtones and apps that are saved to the device. It is recommended that you save (backup) important data before proceeding.
ALTERNATE MASTER RESET METHOD: If unable to reset the device using the above steps, try the Alternate master reset method. With the device powered off, press and hold the Volume down and Power/Lock buttons until the phone vibrates, then release Power/Lock button. Release the Volume down button when the black screen with red and blue lines of text appears.
Press the Volume down button until "factory reset" is highlighted, then press the Power/Lock button to select. The device will reset.