Why does PC to TV via HDMI play no sound in some videos?

I had a similar problem. It took me forever to figure out that my problem was that the TV didn't want to play sound on something I all ready had open. Like my browser. If I had a browser window open with audio on the computer and plugged it into the TV that window didn't get to have audio... Even when the TV was set to be the default Audio device. I think it was some sort of priority thing. Like that window was all ready delegated to the computer speakers.