I searched "you tube +black screen" and found someone had the same
problem that I have experienced:

Hi, I got a problem, whenever i want to play a video, i click on the
video, then that takes me to the screen where it should start playing,
and everything loads right, because i see everything except the video
itself, all i get is a black screen, no audio. I don't even get a
button to press play or pause. its just a black rectangle. Ive
followed the suggestion to uninstall adobe flash, and then reinstall it
with the latest version..and then restart your computer. So iv done
all that and the problem still persists. and i know its not just the
site down because i can get on my main computer upstairs and watch
videos all day long. If you could help me that would be amazing, thanks

Anyone have any suggestions?

One of the forums said after Google acquired You Tube this was the result?

Sammy A.