Hello,
I had this problem but not anymore.
First, your video card should handle sound. My card is an ATi Hd 2600XT and
it has a processor sound built in so I know sound was a possibility.
Second, in Start/Control Panel/Hardware and sound/Sound/Manage Audio
Device/Playback Tab, you should see your Hdmi hardware, my TV is called
Digital Output Device (HDMI), if you doesn't see something close to that
name, try contextual menu option (Show disabled Devices) or (Show
Disconnected Devices). You will have the option Enable, Disable, Test, Set as
Default Device, this last option will allow you to use the speakers of your
TV. Beware, if you enable it, you could loose your TV sound so don't forget
to select what you need.
Good Luck!