Appreciate the suggestion. I did the repair, but videos still don't play.
I tried putting quicktime in "safe mode", but that also did not solve the video-play problem.
However, I downloaded a video and that video does play.
A video may start but quickly freezes.
In itunes is the player "quicktime or itunes"?
When I open the quicktime player(its appearance doesn't look like a player with controls for play, pause, etc.).
Maybe the controls appear when play begins' however, then I try to open any song of video, I always get the same message: "Do you want to allow this website to open a program on your computer(in itunes, I assume).)
If i choose "yes" I get an error message.
I thought this additional information might be helpful, but you can just answer the original question if you have some additional ideas.
Thanks for your help.