I had a black screen last month and that was a reason I couldn't log in.
Only way to fix it for me was this:
Close our software, you will not be able to delete the required files while our software is open.
Press the Windows key.
Type in:
%temp%
Delete the all folders - you can chose to ignore the ones that cannot be deleted as they are being used by other applications.
After this I needed to do this:
In this case, please rename your user (or user.ini) file. You can manually navigate to the settings folder to locate the file:
Press the Windows Key.
Type the following or copy/paste into the area provided and press 'Enter':
%USERPROFILE%\AppData\Local
Locate and open our software's folder.
Locate and rename the 'user' or 'user.ini' file (it can be renamed 'user-old').
Finally, to complete the process, restart your computer.
Maybe this will help for you as well. It's just a guess.
Cheers,
SDK1987