In windows 10 you may find that display manager does not show all of your monitors plugged in.
It appears that MS actually included 2 different display mangers in windows 10.
DO NOT right click the desktop and go to display settings.
1. Go to control panel and select “Display”
2.Select “Project to a second screen"
4.Go back into Display and chose “Change display settings”. (Note: This must be done here and not display manager.)
5.Here you can enable the screens, configure resolution and position.