Also, some TV's have a dual-mode HDMI interface on them to handle people who have DVI inputs (DVI doesn't have the audio on the cable like HDMI does). My JVC is like this ... it's supposed to "autosense" that I have an HDMI plugged into it and use that, but for some reason it kept thinking it was DVI and was looking to the standard audio ports for input.
If you've got a second HDMI input on your TV -- try that once (or look for a setting on the TV which changes from standard to digital audio).
As someone suggested, also try running a seperate audio cable from the box to your TV audio input and see if you get sound -- it'll point out if there's a handshake problem or something else possibly going on.
also some TV's have the abilty to turn off their speakers (for hooking up to a stereo), make sure that the speakers are turned on. this is usually in the TV menu (TV itself, not Verizon menu)