How is the cable box connected? Back in the old days, sometimes it was on channel 3 or 4. These days, HDMI is much more common. A cable box remote may or may not be able to switch inputs on a TV. (Often not in my experience.) If you find a way to make the cable box remote do it, then make a note of the procedure. And/or get a replacement remote for the TV. (You really want a remote that can control the TV in any case.)
Sometimes you get a case of partially overlapping/close IR codes, where a remote for another device in one button press out of a hundred or thousand (and maybe pointed at an odd angle too) gets interpreted as something for another device to do. In those cases, it's easier to grab the other device's remote and put it back than to make that rare thing happen again.
