Need help getting computer to play sound through HDTV.

Okay, I’m trying to figure out how to get sound from my computer to play on my HDTV through an HDMI. The usual instructions are to make sure it is plugged in and enabled, then set it to default. It’s plugged in and enabled, but the “set default” button is greyed out, and it says that it’s already the default device. There is a bar showing that the computer picks up sound, but I can’t hear it at all. The TV works fine on my game system, too.