Perform a soft, factory, and alternate master reset of the device.
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INSTRUCTIONS & INFO
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 key, then tap Power off. To turn the device back on, press and hold the Power/Lock key 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 key for 10 seconds, until it reboots.
If you are having trouble powering down, you may need to Factory data reset (Master reset) the device. This will erase all data on your device and restore it to factory settings. To ‘Factory data reset’ your device, swipe down from the top of the screen, then tap the Settings icon > Backup & reset > Factory data reset > RESET PHONE > ERASE EVERYTHING. 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.
If unable to power off the device using the above steps, try the Alternate master reset method by first powering the device off. Tap and hold Power/Lock Key If your phone will not power off, you will need to wait until the battery is drained of power.
Once the device is powered off, press and hold the Power/lock key and Volume-down key for approximately 3 seconds then release.
From the "Boot Mode Selection Menu" screen, select Recovery. Note: Use the Volume-down key to scroll through the menu options and the Volume-up key to select.
From the "No Command" screen (Android figure lying on his back), press and hold the Power/lock key then press and release the Volume-up key to display the menu options.
Select "wipe data/factory reset". Note: Use the Volume keys to highlight and the Power key to select.
Select Yes -- delete all user data. Note: Allow several seconds for the factory data reset process to complete.
Select reboot system now. Note: Allow several minutes for the reboot process to complete.