Usually a relay clicking indicates insufficient voltage to the starter. Is it the original battery? if so, it's time to buy a new one.
The starter uses more battery than anything else- the lights could work fine but the battery may not have the guts to roll the engine.
try jumping it from a 12 volt battery- if it starts, it's the battery.
It could be a starter, but more likely it's a battery. They usually last 4-5 years.