I received a couple of question this month and one of them jumps out; Stuck on a black screen with a movable cursor.
Ok. I think I know what you mean and this is my work around for it (mentioned before in one of my replies in a blog post):
1.) Press enter (background image flashes shortly).
2.) Enter you password (screen is still black).
3.) There is your desktop.
Well. That’s it. Works every time for me. No matter what display connector that I use (HDMI, DVI or VGA).
p.s. You may run into this black screen with movable cursor if your PC failed to wake up, after you’ve used the on/off switch to boot again.
Update: Apple change something in 10.12.3 Beta (16D30a) and as a result the screen is no longer black.