Youtube goes black fullscreen!

[Macaroooon]

When I go full screen in youtube on Safari 8.0.5 it often goes black or grey and black.

I have the latest flash player installed. I'm running Yosemite.

Why is this?!

 

[GlenK]

Mine is going black screen on anything, even without full screen. I get sound but no video. Even tried Chrome and same thing. I don't get it either. Just started doing that this week!! Updated Flash and Flip4mac and neither helped.