Another tip ...
As an aside... one thing that can cause a "black screen" is to inadvertantly enter a sequence like Ctrl+Alt+F8.
The equally-mysterious way to fix things might be Ctrl+Alt+F7.
Let me explain ...
On many Linux systems, you can have several "virtual terminals," with sessions running in each. Ctrl+Alt+Fn is used to switch between them. Some are terminal sessions. The one at F7 is probably GUI. And there might not be another one at F9-F12. If you switch to it, blank screen. Solution is to just switch again, but there's no clue.