1. To succeed this operation you will need to install official Sony Software called PC suite.
  2. You can download it from here -> Sony Site  
  3. Check device, it must be turned on. Hard Reset SONY ERICSSON P910
  4. Install PC suite software on your PC or laptop , startup appliaction.
  5. Plug in your Device into the USB port.
  6. Now find and select Tools then select Phone repair, find and select your device model. 
  7. Follow up with instalation wizard.
  8. When PC suite will end Factory data reset your handset should restart.
  9. Success! phone is ready to work on.

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

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