Had similar problem with Windows 7 and Toshiba laptop and Toshiba TV, video through HDMI cable but sound out of laptop. Was working fine for over a year (both sound and audio out of TV through HDMI) then one day sound just stopped.
Going to - Start Menu - Control Panel - Sound - Playback tab.
Your TV should be one of the playback devices listed. If not, right click inside the device list box and select 'Show disabled devices'.
Now that TV is listed as a playback device, right click on it and select enable. Then right click again and select 'set as default device'.
Green check mark should now appear on TV icon and sound should now come from TV with video.