The New Version of Mac OS, Mac OS Sierra is making it difficult for old Macs to shut down. It doesn’t seem to be a bug that Apple will patch because at the bottom of the Shutdown dialog is an option that says “Power of this computer from here.” Well, with a menu box checked and a button with words on it, I’m not sure how you’d figure out what’s going on without asking someone. And if you repeat questions often enough, people make assumptions about your intelligence or motives.
Apple has updated their most recent version of macOS – Mojave 10.14 which solves this problem for many people who are still running older versions of macOS (10.7 or below).