External monitors are black, only mouse pointer is displayed

I have gotten a new Macbook Pro today at work. I want to connect it to two external monitors, which I have done. Strangely I can see the mouse pointer on both of these external displays, but nothing else. I can drag a window onto that monitor but it does not appear, only the mouse pointer appears. Strangely I can take a screen grab of that external monitor and it *does* capture the window that I dragged to it, and the desktop image. Still thogh as I look at the monitor it is all black.

This person: high sierra external monitor black with mouse describes exactly the same symptoms but nothing there has helped me to fix this issue.

Any guidance would be appreciated.