When I upgraded, my screen remained black without the cursor for over 10 minutes, after which I decided to go to bed and check on it in the morning. The next morning, everything was fine. It takes a while to do its work, and I just had to give it more time.
Turning it off at this point is not suggested. How long to wait exactly I cannot say, since I left on the computer overnight while I slept. My suggestion is to attempt it again when you can give it that time to work overnight.
Please see the thread
How-to Get Started with Windows 10 which will give you links to further ways to troubleshoot your possible issue.
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