Performing a Hard Reset
Warning : it is impossible to recover your data after doing a hard reset, so online backup is always important. For all of your data, a backup should be done on an external device, hard drive, system or media.
Force Reset the device (press and hold POWER button for 8-10 seconds)
Unlock Galaxy S3 T999 i747 i535 using hard reset
sgs3 hard reset or reset Galaxy S3: PRESS AND HOLD VOLUME UP + Home Button + Power
Turn the phone off
Press and hold Volume UP and Home (center) button
Press Power until the phone vibrates
Wait until you see the Android logo then release all the buttons
Select Wipe data/Factory reset with VOLUME DOWN, press Power (right hand-side)
Select YES…delete all user data with VOLUME DOWN and then Press Power
After format, press Power again to reboot the phone (select reboot system now)
or Use this method to reset your Samsung Galaxy S3: Enter *2767*3855# WARNING: All fo your data (contacts, messages….) will be lost! Make sure you complete a backup before starting ( Carbon Backup is a good one). Take out SIM card before full reset too! As a rule, this shouldn’t delete the data on your external SD card.
Attention: if you reset your device to the factory default with SD card encryption setting enabled, the device will not be able to read your encrypted files. Disable this setting before resettling the device.
SGS3 Firmeware Flash downlaod mode: PRESS AND HOLD VOLUME down + Home Button + Power On
CAUTION: Perform this reset AT YOUR OWN risk!