Is your rooftop antenna active or passive? If active, it will have its own power supply and onboard electronics which can eventually fail. If passive, there's not much to go wrong other than corrosion where the cable meets the actual antenna element.
I've seen DTV tuner/converter boxes "forget" a station at random; sometimes several. Usually unplugging, waiting half an hour, then performing a channel scan will fix the problem.
You shouldn't need a balun. That's used to match impedance, usually between 300-ohm twin-lead and a 75-ohm coax input. Not real common on new installations.