My first guesses would be that the cable box failed, or the cable company removed access. Of course, it could be the TV tuner. You can avoid the TV tuner and cable box RF modulator by switching to an HDMI connection. (Which should also produce a huge improvement in picture quality.) If there is no HDMI out on the cable box, then perhaps just swap out the cable box for a modern one? I would think that any cable box designed within the last 15 to 20 years would have HDMI. Cable companies love to keep collecting rent on ancient equipment that was paid off years ago, so sometimes you have to let them know that you're one of the customers who actually notices things like that.
