This procedure will hard reset or restore back the Samsung Galaxy S3 or S III GT-I9300 to it's original factory default settings. This process is useful if you experience some lag, frozen or unresponsive issues. This is not advisable on some part, for it will wipe and delete all data stored from your Samsung Galaxy S3, so just ensure to make a back-up copy of all of the important files you had on your device.
Samsung Galaxy S3 Soft Reset and Hard ResetIf the phone freezes, the most often method is to remove the battery out after a couple of seconds and then putting it back again.
Hard Reset by CodeYou can directly reset your device by typing this code *2767*3855#, this will reset your phone automatically once rebooted.
Hard Reset by button combination
Sometimes the code may not always useful specially when your Samsung Galaxy S3 is frozen and become unresponsive or in other sever unresponsive problem like it just stuck on welcome screen logo.
To fix it, just then again remove the battery out, then put it back again. Don't power it ON yet, just press and hold the Volume Up, Center button and Power button at the same time.