Hard Reset SONY Xperia Z5

First method:

1. Start by switching off the cell phone by holding down the Power button. 
2. Afterwards go to Settings and then to Backup & Reset.
3. Then selec Factory Data Reset and tap Reset Phone.
4. Choose Erase Everything if you are sure you want to clear all your data. 
5. In the next step select OK to confirm the whole operation.
6. Congratulations! The hard reset has just been performed.

Second method:

1. First you should download flashtool from Sony website:http://developer.sonymobile.com/services/flash-tool/
2. Make sure, that you have installed drivers for your USB data cable.
3. Now turn your device off.
   
4. Then press and hold Volume Down, and connect to USB cable.
   
5. Follow the instructions on your screen, and accept appropriate options.
6. Success!

Third method:

1. First you should download PC Companion, in example from here:http://www.sonymobile.com/gb/tools/pc-companion/
2. Install it and run.
3. Next you will see window with 4 options.
   
4. Choose option "Support Zone New!", and click "Start".
   
5. Wait for the program to install the appropriate add-on.
6. After that you will see next window with 3 options.
   
7. Go to option "Phone / Tablet Software Update", and click "Start".
8. Select "repair my phone / tablet".
   
9. Now follow the instructions and accept all informations. 
   
   
10. Please be patient and wait until preparing computer for software update is complete.
    
11. Afterwards choose your phone / tablet model.
    
12. If you see this window, then connect your device into your PC.
    
13. Great job! Your device is ready to use.

Fourth method:

1. If the display is off, press the Power key to turn it back on.
2. In the next step open the phone's dialer and type in: *#*#7378423#*#*.
3. From the menu which should appear on the screen choose option Customization Settings and then Reset customization.
4. Confirm information: "data will be cleared and factory data reset will perform".
5. Accept by pressing Reset customization and reboot.
6. Well done! You have just performed the hard reset operation

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