I woke up this morning to a blank (black) Apple Cinema Display screen. I thought it was asleep as usual, but it didn't respond. I turned off the computer and turned it back on. The screen flashed in a horizontal line and then went black. After that one flash, subsequent re-startings of the computer have done nothing to the screen. I have a Apple Cinema Display and a MacPro computer, both c. 2011 or 2012. I bought them through Craigslist 2 1/2 years ago, and they have worked fine until today. The MacPro is running the latest El Capitan system. I thought I would test the display with my Macbook (early 2011)—so I plugged in the display plug (thunderbolt + USB cable that came attached to the display) to my laptop. Nothing. It seems to see it in systems preferences because if you go to "displays" it says "LED cinema display". But is there something else I need to do to get the display to come to life? Some mysterious command, or turn the laptop on and off?? Then I thought I would check the computer itself. When I turn it back on, there is the familiar "ding" as it boots up, but that's it. I tried accessing it through wifi and my laptop, but when I go to "connect to server" the laptop doesn't see it. So I can't get to the computer. So now I'm completely baffled--is the problem the display or the computer? Or both? What do I do??? I should add I have read all the Apple help material. It wasn’t helpful. It assumes you haven’t plugged the equipment in, or you have messed with the cables, etc. etc. This has been set up the same way for 2 ½ years and has worked fine until this morning.