Entertainment Center Upgrade

If I remember right, the coax to the antenna should have a connector at the antenna. Climb up there and disconnect it and the cable where it goes into the back of the wall plate. Then ohm it to make sure it isn't shorted. Then short it and test the other end again to see if you can read the short through the cable. If the cable is good, you could use a set of rabbit ears to the TV and see if they'll pull in any stations. If that works, connect them to the cable at the antenna on the roof and bypass the wall plate with the other end straight to the TV and see if you can still do a successful channel scan. Prove the cable is good before condemning the antenna.