How To Fix Samsung Galaxy S8 Side Button Not Working (Power Button Problem)
Some users of the Galaxy S8 have reported complaints of the side button that controls power has a tendency to stop working or falter. The button can jam or simply not respond when pressed. Some users have said that in their experience the lights on the phone can activate when the button is pressed but the screen does not.
There are also cases of the phone screen turning black during phone calls, which is believed to be related this issue on the Galaxy S8 and Galaxy S8 Plus.
How To Fix Galaxy S8 Side Button Not Working
The first thing you should do is try to run the phone in safe mode. It is possible that a recent download has caused the issue. Running safe mode will identify this for you, and allow you to delete recently downloaded apps. (Learn how to get Galaxy S8 in and out of Safe Mode).
You can also try resetting your Galaxy S8 to its factory setting. Once you have completed this reset, you should try and have the latest update available fully downloaded before continuing to see if there are improvements.