Phone playing up?
If your Galaxy S II keeps freezing, you’ve forgotten the security codes or it just doesn’t work, take it back to factory settings.Important: This wipes everything on your phone, so if you’re not locked out try backing it up first. This won’t wipe your SIM.
Turn the phone off. If you can’t, remove and reinstall the battery.
With the phone still off, hold down the Power, Volume Up and Menu buttons at the same time for about 10 seconds. Release them when you see the green android logo. This’ll get you into the unlock/reset menu.
Scroll down and select 'Wipe Data/Factory Reset'.
You can use the volume buttons to scroll up/down and the power button to confirm selections.
Select 'Yes – Delete All User Data'.
Select 'Reboot System Now'. The phone then reboots to factory settings with the security lock removed.