The black screen is a known issue and LM are working on a fix
Its usually caused by exiting out of the application while still in full screen mode. In the meantime you have two options.
1.simply delete the prepa3d.cfg file and rerun the sim. Everything should work fine.
2. When the sim running, ALT+ENTER. to get back to windowed mod. The screen will still be black. Now, exit out and rerun and your back to normal.
LM stated that it might have something to do with HDR but I've got it on and its works unless I forget and close the programme while in full screen.