The clicking is a solenoid (basically a relay). There is probably enough power (charge in the battery) for the electrical system but not for the starter. When the starter is energized, the additional current loads the battery and the battery voltage drops.
There are three ends to the positive battery cable (alternator, starter, battery). Check the cable ends for corrosion. A corroded battery cable can cary just enough current for radio and lights, but not enough for the starter.
The battery has six cells. One or more cells may have dried out a bit over a couple months, and are low on fluid and therefore too weak to charge properly.
Top up the battery (preferrably with distilled water), clean the battery terminals, jump the car if necessary, and drive it for an hour to get a good charge. Even after that, it can take a couple trips to charge it fully.
There are three ends to the positive battery cable (alternator, starter, battery). Check the cable ends for corrosion. A corroded battery cable can cary just enough current for radio and lights, but not enough for the starter.
The battery has six cells. One or more cells may have dried out a bit over a couple months, and are low on fluid and therefore too weak to charge properly.
Top up the battery (preferrably with distilled water), clean the battery terminals, jump the car if necessary, and drive it for an hour to get a good charge. Even after that, it can take a couple trips to charge it fully.