Projector displays an empty desktop

For Macintosh: Make sure your additional display is properly connected and powered on. From the Apple () menu, choose System Preferences. From the View menu, choose Displays. Click the Arrangement tab. Enable (check) "Mirror Displays" in the bottom-left corner. Source: https://support.apple.com/en-us/HT202351
Published on: 2015-10-21 See other articles in Projector.