If it were a real button, I'd have to say that it's broke, but of course, it is not.
But since back around Win-98 I've used a Quick Shutdown shortcut Icon on my desktop or quick launch tool bar. (taskbar)
The syntax for the Quick Shutdown has changed a little over the years, but it's not changed since Win-8.1.
Here's the syntax for the Shortcut I use to shut down my computer(s).
%windir%\System32\shutdown.exe /s /t 1
There are three spaces in that line, but they should be apparent, and necessary.
Make a desktop shortcut with that command line, and see if that won't shut down your computer for you.
Good Luck,
Shadow