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  • Start by turning on the device by holding the Power key for a short while.
  • In the next step find and select Settings and tap Backup & Reset.
  • Afterwards tap Factory Data Reset and then Reset Phone. 
  • Choose Erase Everything if you are sure you want to clear all your data. 
  • Next, select OK to confirm the whole operation.
  • Well done! The hard reset has just been performed.

Seconds method:

  • First of all, you should download PC Companion, in example from here: http://www.sonymobile.com/gb/tools/pc-companion/
  • Next, install and run this application.
  • Then you will see window with 4 options.
  • Choose option "Support Zone New!", and click "Start".
  • Wait for the program to install the appropriate add-on.
  • After that you will see next window with 3 options.
  • Go to option "Phone / Tablet Software Update", and click "Start".
  • Select "repair my phone / tablet".
  • Now follow the instructions and accept all informations.
  • Please be patient and wait until preparing computer for software update is complete.
  • Afterwards choose your phone / tablet model.
  • If you see this window, then connect your device into your PC.
  • That's all

Third method:

  • At first, download the flashtool from Sony website: http://developer.sonymobile.com/services/flash-tool/
  • Make sure, that you have installed drivers for your USB data cable.
  • After that, power off your device
  • Then press and hold Volume Down, and connect to USB cable.
  • Follow the instructions on your screen, and accept appropriate options.
  • Success! Your phone is ready to use.