Several HD channels do not function

Hello,

Several of my HD channels do not function. They will either have sputtering audio and pixelated pictures, or say "Temporarily Off Air." The Standard definition channels work fine. I've tried restarting the box, reconnecting the cable cord, to no avail. My cord is not connected to the receiver through a splitter. It's the only TV we use in the house. Any suggestions? It makes football watching on the HD channels impossible, for example.