Here's what to try first. A simple restart.
Try and power off the phone. I know with my s7 you need to enter a passcode before turning it off, so see if that works, and if it does, then you can try turning the phone back on and seeing if it works then.
If that doesn't work, report back and we will try and find other options. I want to try and figure this out before we go with what Scott said about factory resetting the entire device, losing all your data.