Samsung Galaxy S II hard reset
Press and hold Volume UP + HOME + POWER. Select factory reset with volume down. Press power to reset.
Use this method to hard reset your Samsung Galaxy S II: Enter *2767*3855#. Warning! All your data including contacts, messages etc. will be lost! Copy all your necessary data/Contacts/Messages etc. to SIM or make backup to your PC before full reset! Take out SIM card before full reset.