Windows 10: Windows 10 Lockscreen is just.. black..

Since a day I have the following scenario:
When I lock the screen, a black screen comes up.. and after about 10 - 15 seconds the login screen comes back up.
I tried to switch to background image instead of the Windows Spotlight, but that didn't make a difference at all.
Clicking or typing (when the black screen is on) doesn't help anything to get to the login screen either... *Huh

Anyone any idea what I can do to solve this -strange- issue?

(I know it's vague.. but that's all I have for now... The only thing different from yesterday is that I installed an old game (1999) with windows 98/me compability (the installer.. that's it).. but I doubt if that would have consequences for the lockscreen..)

:)

 

Lock screen settings won't change, no error message.

Thank you for the detailed response zdzdz, I'm glad it worked for you.

I tried the steps you listed and it didn't fix it for me. It did remove all my existing lockscreen images, so now I just have a black screen as the lockscreen. I can't even change this black lockscreen back to the picture slideshow now. Gaaahh Windows.

 

Lumia 535 blanc start screen background

My lockscreen is also affected, not showing any images but just showing a black screen with no images.