How do I start my Samsung Galaxy S3 in Safe Mode?
You can boot up your Samsung Galaxy S3 in Safe Mode if you wish to troubleshoot whether or not added applications are causing problems with the Samsung Galaxy S3. Safe mode will load only basic system software.
Make sure your device is turned off.
Press and hold the Power key to boot up your Samsung Galaxy S3.
After the start-up animation begins to display, press and hold the Volume down key.
When the lock screen is displayed Safe mode is displayed in the lower-left corner of the screen. To boot your Samsung Galaxy S3 in normal mode again restart your device.
Another way maybe help you: