Hard Reset ZTE v791

First method:

1. Power off the phone.
2. Next turn on the device.
   
3. Choose emergency dial, and type this: *983*22387#
4. Select from the menu Erase Everything.

Second method:

1. Switch on the cell phone.
   
2. Now from the home screen choose: Menu -> Settings -> Privacy -> Factory data reset ->Reset phone -> Erase everything.
3. Then your handset will reboots.

Third Method:

1. Make sure, that your phone is off.
2. Now press and hold this buttons: Volume Down + Volume Up + Power key.
   
3. Next from the menu choose "Wipe Data/Factory Reset", using Volume buttons to scroll to option, and Power button, to confirm operation.
4. Then select "yes", and confirm with Power button.
5. After that press Power button to enter option "reboot system now".
   

WARNING !
Hard Reset will erase all of your data
All described operations you are doing at your own risk.