Hey guys my name is Alex, Im new to the forum. Today when I jumped on my Macbook and was watching a youtube video i tried to turn down the sound using my sound button in the upper right hand corner.. but nothing happened. I could see the sound bar that pops up in the middle of the screen go up and down but the sound stayed where it was. This is new and has never happened before.. Has this happened to anybody, and does anybody know how to fix it? 