The only problem was, it had no display.
If you pressed the home or power button the menu lights would light up, but there was nothing on the screen. It just sat there with a blank black screen.
In this case, the phone needed to be restarted.
To restart the Samsung Galaxy S7 you need to simultaneously press down on the volume down and power button at the same time. Hole these two buttons down until the phone restarts. You may have to hold them for 4 or 5 seconds before the phone resets.
Here is a video which shows the process as well.