I have a Soyo MT-SYTPT 4227ab LCD TV and a Toshiba Satellite A300 PSAG8C-048013 laptop (Mobile Intel® GMA 4500M graphics).
When I connect them via HDMI, I do not get any audio. When I connect my laptop to other TVs the audio works and I see a new audio device. With the Soyo TV, I do not see an audio device. Therefore, I believe there is some sort of incompatibility between my TV and Windows 7 or graphics card.
However, previously my Xbox 360 also had this same problem. I found this thread http://forums.xbox-scene.com/index.php?showtopic=631109 which describes a problem in which the Xbox 360 is not getting a response from the TV so it defaults to DVI output (no sound). I was able to disable display detection and my sound started working. There has to be something similar I can do for my laptop.
I also have a Patriot media box, which I tried with this TV, it outputs HDMI audio with no issue. It's frustrating that a simple media box can output HDMI audio to a problematic TV while a laptop with an Intel graphics card cannot.
I have the latest video drivers.
Turns out the TV was sending bad EDID.
Found a solution, just posting in case this information can help others.
See my thread at AVS forums: http://www.avsforum.com/t/1414129/modify-the-edid-of-lcd-tv-to-enable-hdmi-audio-output