I've looked online for fixes including things like disabled sleep on the display, disable monitor sleep in OS X and that seems to have fixed my issue until I upgraded to 10.11.3 and now my display just doesn't work in OS X anymore. In fact I can't get it to work with my Mac Pro or my 15" MacBook Pro, whereas it was mostly no problem before (after doing the all the stuff above). Now, when I boot up the computer, and it will just be blank, so I can't see the login screen or anything. But if I boot into Windows , it will work perfectly. Any ideas?