You can use the Safe Mode feature on your Samsung Galaxy S4 to access the operating system with default software. Use Safe Mode if you have installed something on your S4 that no longer allows the device to start successfully. Just use these steps.
To turn on Safe Mode, follow these steps:
1. Power the phone off.
2. Once the phone is off and all lights are emitting, press and hold the Power button to turn the S4 back on.
3. When the Galaxy S4 logo appears on the screen, press and hold the Volume Down button.
4. Continue to hold the Volume Down button until the phone completely boots. You will see the words “Safe Mode” appear in the lower left corner of the screen if you performed the steps properly.
While in Safe Mode, you may not be able to use certain features or applications. The device is in a “bare bones” state where just the essential software is loaded. This allows you to get into the device quickly, enable or disable whatever you need to, then restart.
To turn off Safe Mode, a simple restart should do the trick. Some users are reporting that it doesn’t though. In this case, remove the back cover and pull the battery from the device. Leave the battery out for about 60 seconds, then place the battery back in, assemble the rear cover and start the phone again.
Some Galaxy S4 models may require you to press and hold the Volume Down button during startup in the same manner as enabling it to exit Safe Mode.
That’s all there is to it.