Assuming your Java is up to date....
Un-install Flash player using the proper Adobe un-installer.
Go to Adobe site.
Click to install flash player 10...but DON'T run it....SAVE it to your computer somewhere.
COMPLETELY exit browser.
Go to location of saved flash player.
Run the installer.
Then go back to you tube and it should play.
Assuming your Java is up to date....
Un-install Flash player using the proper Adobe un-installer.
Go to Adobe site.
Click to install flash player 10...but DON'T run it....SAVE it to your computer somewhere.
COMPLETELY exit browser.
Go to location of saved flash player.
Run the installer.
Then go back to you tube and it should play.