First method:
- Press Power button until your phone is on.
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- Next go to Settings -> Backup & reset -> Factory Data Reset -> Reset Phone -> Erase everything.
- Confirm that operation.
- Done!
Second method:
- Download program named flashtool from Sony website: http://developer.sonymobile.com/services/flash-tool/
- Then check, that you have installed drivers for your USB data cable.
- Now turn off your handset.
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- Afterwards press and hold Volume Down, and connect to USB cable.
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- Accept all informations.
- The end.
Third method:
- You should first download and install program PC Companion.
* In example from here: http://www.sonymobile.com/gb/tools/pc-companion/
- If all went well, you will see window with 4 options.
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- Next click "Start" under the name "Support Zone New!".
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- Wait until the process of the installation is completed.
- Now you should see window with in example option "Phone / Tablet Software Update".
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- Accept this option -> click "start".
- Then click "repair my phone / tablet".
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- Please follow all instructions, and confirm that.
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- Read "Inportant information", and confirm.
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- Afterwards PC Companion is "preparing computer for software update".
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- Next select your phone / tablet model.
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- Follow steps, which you see in new window.
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- That's all!