It seems that Lightroom process is not getting closed properly, which is why the process is running the background.
Could you please try, right click and select run as administrator to Lightroom application, then try to close it again and see if this helps.
Ran as Admin and had the same result. Process still running and cannot restart.
Please follow the below steps.
> Quit Lightroom.
> Navigate to the location of the catalog.
> Move the catalog to a different location(e.g. Desktop)
<Now Lightroom will not be able to find the catalog and will ask you to create a new catalog>
> Create a new catalog and import few images
> Quit Lightroom to check for the issue.
I have this exact same problem, after closing LR it creates a background LR task and the next launch fails (spinning cursor). Stopping this task allows LR to relaunch. Windows 10
That cracked it!
Fixed mine too. Then I imported photos from "import from another catalog" all seems good now.