Folks running older computers, and seems especially Windows 7 over four to five years old are having problems big time.
28 pages of black screen freeze faults when trying to install Windows 10 here :-

http://www.tenforums.com/installation-setup/9249-windows-10-install-stuck-black-screen-without-cursor-anything.html

If you haven't made a full back up such as a complete image to an external hard drive, then you are stuck as nothing works and you cannot roll back. It happened on my laptop. Thankfully I maintain image backups, so could revert back using the image.