Car won't start — just clicks once then nothing

Before you buy a starter: check the battery cable connections at both ends. The positive cable bolts to the starter, and the negative goes to the engine block ground. Corrosion on either connection can cause exactly this symptom. Clean them with a wire brush and try again. Free fix if that's the problem.

Single click with strong electrical = starter motor or starter solenoid. The battery has enough juice for accessories but the starter draws 100-200 amps. Either the starter solenoid contacts are burned (super common on Toyota starters) or the starter motor itself is seized. Try tapping the starter with a hammer while someone turns the key — if it starts, the starter is on its way out and needs replacing.