Best answer by djames
1. If your Samsung Galaxy S II is frozen, Shut the POWER OFF, take the battery out and put it back again.
2. Hold the Volume Down button
3. Briefly Press and release the Power button
4. A menu will then appears that let you allows for Fastbook, Recovery, Clear Storage, and Simlock
5. Select Clear Storage by pressing the Volume Down button
6. Quickly Press and release the Power button
7. Select Volume Up for YES and Volume Down for NO
If the above procedures doesn't work. try this another method:
1. Turn the POWER OFF, pull the battery out and put it back again.
2. Simultaneously press the Volume Up, Home and Power button
3. If the Samsung Symbol appears, release the Power button
4. A Boot Menu will then show, Use the volume up/down to choose and home to select.
Let us know if this works.