Two options.. IF you are the original owner only one
Bad coax The coax likely runs in two runs. From the box with the light that comes on to the roof. and from the roof to the antenna.. ON MY RV doing routine roof maintenance I tore up the connection in the roof (It was kind of nasty anyway since moisture had gotten to it and rust happens.. I put on new ends and a new barrel connector (Double female) sealed it up to water proof (I do that real good) and .. i'm watching Recorded OTA TV from about 45 miles out as I type.
But if you have no power to the head. that's suspect 1 2 and 3