I'm a novice with using Cura.   A few weeks ago, when I use Preview mode, I got the simulation player and could check exactly how a model would be printed. Recently, it's stopped showing up. I've check the setting of "Force layer view compatibility mode" which was mentioned in this thread. Since it worked a couple of weeks ago, my GPU (NVIDIA GeForce 730M) must support a suitable version of OpenGL. I am on the Windows Insider Preview program, so it's possible that's broken it.