It's probable faster to have Technical Support take a look at what's happening as it's difficult to judge from here.
I can only guess that there is some other software interfering with it...perhaps.
They are free by phone and linked here:
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We have noticed this whenever there is an unwanted Program present in the PC (See PUPs - Potentially Unwanted Programs - Basics)
Can you try the below when the screen starts black
Press CTR+SHIFT+ESC to bring up the task manager
Click on File > New task (Run) > Type explorer.exe > Click OK
Check if your desktop gets loaded.
Thanks Selvan, didn't realise that you were back ;-)
I tried to press ctr+shift+esc but nothing happened. I think, the computer is "frozen" bevore the login screen. Is it helpfull to post a Preinstall Tool log?