Unless you're forcing YouTube to use Flash Player (via some add-on) it defaults to using the HTML5 player.
I'll need to get some log files from you to troubleshoot further. Please review the FAQ Where do I find the Flash Player installation log on the Macintosh? and provide all 4 files listed. Upload the files to cloud.acrobat.com/send using the instructions at How to share a file using Adobe Document Cloud and post the link to the uploaded files in your reply.
I have a similar problem but in my case the installer bounces when I double click it but it doesn't do anything. I've looked in the var/log/installer file and it doesn't generate anything.
Thank you for your quick response. I don’t have the skills to perform all the tasks you required. I am waiting for my friend to return from her vacation. She will help me with your directions.
So we will get back to you next week.