Galaxy S2 i9100 hardware reset manual:
If you want to hard reset your Samsung I9100 please follow this:
1. Press and hold Volume UP + Home + Power button together.
2. Release all buttons once Samsung Logo comes one.
3. After a bit it shall ask you to enter a password.
4. Enter wrong password about 5 or 6 times.
5. Before entering the password, a warning sign will come that you will lose all your data on SD card.
6. After enter the wrong password last time, phone will enter into boot menu.
7. Select 'wipe data' option, it will tell you to confirm again.
8. After wipe off, boot menu will give you option to reboot phone.
9. Hard reset is done!! Piece of cake. Right!