Hard Reset SAMSUNG I9100 Galaxy S II

First method:

1. Remove battery, and put in after 10 seconds.
2. Press Volume up and Home button in the same time.
   
3. Holding Volume and Home button press Power button for 3 seconds.
   
4. When you will see Recovery menu choose "wipe data/factory reset" using Power button to accept and Volume buttons to navigate.
   
5. Next accept option "Yes -- delete all user data".
   
6. After that confirm option "reboot system now".
   
7. Done!

Second method:

1. Make sure, that your phone is on.
2. Go in to Menu.
3. Choose Settings -> Privacy -> Factory Data Reset
4. Choose Reset Phone

Third method:

1. Turn on phone.
   
2. Press *2767*3855# on dialpad.
3. Turn off and turn on phone.

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