On my main account using IE 10 I can view the video on YouTube but no sound. I have a guest account and YouTube works properly on there. I am running Zone Alarm AV, and I have added YouTube to my trusted sites. I have an i7 - 2600 at 3.4 GHz.
The non sound on Youtube problem has been happening for a couple days and it is happening to a lot of people. Youtube knows about it and is working on fixing it, just be patient.