jdagg might be in the right area to fix this. I've done this with my girlfriends laptop (Sony). If you have the sound/speaker icon in your task tray (bottom right), right click on it and go to Playback Devices. You should have options for Speakers/Headphones, Digital Output Device (HDMI Out), and possibly others. If you don't have the HDMI Out option it's probably disabled. If it isn't listed, right click on one of the options or a white area and choose Show Disabled Devices. It will then show and you can right click on it to Enable it. If it doesn't show then it's probably a driver issue. If it is listed you might try right clicking on it and choose Set as Default Device. Try connecting to your TV then and see if you have sound.
It could be a lot of things, but the above is where I'd start. Or just have Saul look at it.