I have two guesses. And you need to check them in the order I list them
First: The connection between the antenna and the power supply (The box with the light) is a coax cable, actually 2 of them. This is one wire surrounded by another.
Many times I've gone to plug in a coax cable and messed up, bent the center conductor so it touched the outer (nut) conductor and shorted the cable.
Check the connection at the antenna, and at the roof (There should be a feed through in the roof) unless the caulk on the roof is very old (WHich means they reused the original cable)
If it's shorted.. it won't work
BUT.. Before you go up on the roof, Pull the wall module and with the cables pointing down, looking at the back of it, remove the LEFT MOST cable.
Up on the roof with your multimeter check for a short, center to nut. No short, good, re-connect (Carefully) go back downstairs and re-connect.
now.. Replace the fuse that feeds the power supply. (Where that is, I can not tell you but logically it's in the main fuse panel for the house... Or not.