Why does the black screen with cursor only problem apear?

QInG_OfThAtgAmE162

Prominent
Apr 2, 2017
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Hello Guys,
I had a problem with my PC today,
After loging in normaly the screen was black and there were only the cursor... I did some research and it found much about this problem and finally fixed it.
But there is one thing I never read
WHY does it apear? That's my question. Please answer if you know.