Where the video shold be there is only white- you can right click on it and get "about Adobe flash player 9" but no video plays.
I have the latest Flash player (which works with other stuff) and IE7 up to date.
I have also uninstalled/reinsalled flash player using their prescribed method.
I browsed the youtube help forums (which suck ass) and at the very end one other person posted about this exact same problem- but no replies to it yet.
Have also updated Java and made sure it was "active" in custom security settings.