The number 1 cause of this issue is windows resetting your display setting.  This seems to happen at random times, but is a simple fix.  This happens when you have more than 1 monitor(as far as the computer is concerned your projector is another monitor).  So when you come in and find your screen black, then turn on your projector and your desktop should be there.  At this point there are 2 options #1 in another article I explain how to make a display switch.  Very easy to make and use.  #2 Right click on a blank spot on the desktop, click on display settings, under Multiple Displays use the pull down and choose extend if you want the 2 screens to show different things or choose duplicate if you want them to show the same thing.