My issue is that I can't get the sound in my TV which I connected via HDMI. I used ubuntu 12.10 and ATI HD6770. I'm totally new in ubuntu. Who can help me?
First check to make sure there is an HDMI output listed and selected under Sound Settings.
If you don't see one, you'll need to install the proprietary drivers for your graphics card with the instructions found in this answer. Open a terminal by pressing Ctrl+Alt+T on your keyboard and copy and paste the commands in line by line.