Why won't my cable work on my HDTV?

TV Input: I have a 42 inch Panasonic Viera HDTV in my room. Today, I was supposed to get Time Warner Cable on that TV, but no cable box. To do that, the Cable Guy had to install a double-wall cable outlet (for me and my brother's room). He hooked everything up and then, I went to change the input to "TV". On this TV I have 8 inputs: TV, HDMI 1, HDMI 2, HDMI 3, Component, Video 1, Video 2, and PC. I tried to change the input and the input "TV" was grayed out (I couldn't click on it). I am wondering why this happened. Is it a problem with my TV? Or a problem with the cable? How can I fix it?