You are right about the clicking noise indicating that there is a problem with the battery. The most common cause of this problem is that the battery posts have become corroded. Take the cables off the battery, and clean the inside of the clamps, and the outside of the battery posts with a wire brush or a battery clamp cleaning tool. When they are thoroughly clean, put the cables back on, and tighten the clamps securely. If the clicking still continues, have the battery tested with a load tester.
When a battery reaches 4 years old; it may fail suddenly. In those situations, it may still have enough power to run the radio and gauges, but not have enough power to run the starter. The battery could also have gone dead if your alternator had stopped working; which would have led to the battery becoming discharged while the car was running. In that case, the battery could be revived by charging it with a battery charger; but you would then need to replace the alternator.
I hope this helps!!!