I had 4 new Dell, Optiplex 5050 machines that were experiencing this horrible black screen. After two weeks and multiple fixes suggested, I finally found a fix that worked. This is the fix:
I found a fix for this issue through following steps.
For issue were you are getting black screen with white cursor
>Press Ctrl+Alt+Del
>Go to ‘Services’ tab
>Look for ‘AppReadiness’
>Right click and stop it.
Make sure you disable the same after login into Windows.
>Click start and type ‘Services’
>Look for ‘AppReadiness’
>Right click and select ‘Properties’
>Startup type should be set to ‘Disabled’
>Set the ‘Service Status’ to Stopped.
This solution worked for me. Let me know if this worked for others as well.