Hello! I have a problem with my external display; after recently downloading Sierra 10.12.1 with the hope of it fixing my wifi dropping out at random times (it didn't...) my external display (an Acer) became so extremely dimmed that it's pretty much black. I own an macbook air 11" and used the external display to mirror my screen. I use a mac dongle, and it worked just fine before, but now the screen is extremely dimmed when I connect it; when I hold a flashlight close to the screen I can actually see my laptop screen mirrored on the external display, but it's so dark that it pretty much looks black when you look at it normally. Any ideas how I can solve this? Or is this simply a bug that needs to be fixed? Using the buttons on the display itself to increase brightness didn't work either. It stayed dark. help!