I have been using a Samsung external monitor with my late 2013 MacBook Pro and this morning, it went black and won't wake up. When I open the MB, I get a display on both. Close the MB and the Samsung goes black. Checked the settings in Displays and the Samsung is set for 1900 x 1080, and the sleep time is 1 hour. Disconnected the Samsung, restarted the MB and got the same result. Is there some setting I am missing? Works ok with MB open as it is right now. Thanks.