YouTube videos don't work despite installing Flash Player
You need to remove Youtube's HTML5 trial in order for the flash player to work and remember your preferences.

First join the trial, and then leave it. Leaving the trial is the only way to force YouTube to remember you want the videos played in Flash, but of course to do that you have to join the trial first. It fixed the issue for me.

Here's the link:


  http://www.youtube.com/html5


If all else fails, try using other browsers (Google Chrome, Mozilla Firefox etc.)