I have a Apex 47' Flat Screen that is hooked up to a DirecTV receiver via an HDMI cable with no sound.?

The DirecTV is hooked-up to my stereo system and the sound comes out of my stereo and the TV. But, just a week ago, the sound stopped coming out of the TV. There is only one connection from the TV to the DirecTV box, and that is one HDMI cable. What is the problem? Also, the DVR is connected to the TV with one HDMI cable, and the sound is alright with both the TV and stereo system. So it is not a problem with the TV audio. But, there is no sound with the TV when look at normal DirecTV stations -- only a great picture. Is it possible that an HDMI cable can go bad and only display the image and not the sound? Need Help!!