Here is the trick.
Step 1: Turn the mobile phone OFF (If it is turned ON)
Step 2: Press and hold “3”, “*” and Call key.
Step 3: Turn the mobile phone ON (Holding the keys).
Step 4: Hold on the keys for 5-10 seconds.
Leave the keys and your mobile phone will have formatted.
(Precaution: Your mobile’s battery should be nearly full otherwise if battery is low then there may exist any damage)
Use trick and Enjoy…