Hard Reset SONY Xperia Arco S

First method:

1. Power on the phone.
   
2. Then goto Settings -> Backup & reset -> Factory Data Reset -> Reset Phone.
3. Now select option "Erase everything", and confirm that.
4. Done!

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 off your device.
   
4. Then press and hold Volume Down, and connect to USB cable.
   
5. Next follow the instructions in your screen, and accept appropriate options.
6. Success!

Third method:

1. Switch off your cell phone.
   
2. Next hold and press Power button + Volume Up for about few seconds.
   
3. Release them, when you see menu on your screen.
4. Now follow the instructions on your screen.

Fourth 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. Goto 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. Done!

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