I am trying to use an external display with my early 2014 macbook air. My mini-display to hdmi cable and the monitor works with my other windows laptop. Everytime I connect the monitor to my macbook air the monitor stays black, but the laptop display works. The mouse moves to the external display, but I cannot see it. From System Preferences -> Displays, I can see my monitor's name and change the resolutions, but the monitor is still dark. I had the laptop connected to AC power outlet the whole time. Any ideas?