The ZTE phones use the same general key combination to enter Recovery to use Factory Reset option. Charge the phone to 85 % and then turn it off. Press Volume + and Power in the same time then access Recovery Menu. Select Wipe Data/Factory reset and reboot the phone. You will lost all your apps and custom settings, but the this way you will restore access to your phone. Custom content is also preserved (music, videos, images, custom files, etc).