Samsung GT-i9100 Galaxy S2 hard reset with buttons Galaxy S2 factory reset after rooting

PRESS AND HOLD VOLUME UP + Home Button

Keep pressing these 2 buttons + press Power button for 2-3 Seconds
Release only power button, but KEEP pressing Volume up + Home Buttons
With Volume down select wipe data/factory reset (3rd) > Press Power
(VOLUME UP + HOME + POWER buttons)

OR

Your Samsung Galaxy SII device freezes or has fatal errors

If your device freezes or hangs, you may need to close programs or reset the device to regain functionality.
If your device is frozen and unresponsive, press and hold  for 8-10 seconds. The device will reboot automatically.
If this does not solve the problem, perform a factory data reset. In Idle mode, open the application list and select
Settings → Privacy → Factory data reset → Reset phone → Erase everything.
OR
Use this method to hard reset your Samsung Galaxy S II phone: 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 on your PC before full reset!
OR
1. Turn off the i9100 S 2 phone or take out the battery and reinsert it.
2. Hold the Volume Down button
3. Press and release the Power button
4. Select Clear Storage by pressing the Volume Down button
5. Press and release the Power button
6. Press Volume Up to confirm i9100 master reset
I9100 Download mode when you reflash galaxy s2 firmware, root
Turn off i9100. Press and hold VOLUME Down + HOME + POWER buttons together.