I’m a moron. The cable was stuck on Channel 3. I did everything I could to fix it, including Googling the problem. Then I called a tech at Comcast. He worked with me for about a half hour. Nothing that he did worked. I was very frustrated, and, I believe, so was he. Then I looked on the arm of the couch and saw the cable company’s remote. I had been using the wrong remote, which worked to turn the tv off, and work the volume strangely.