car will not start: what the symptom tells you

what the car does when you turn the key narrows it down enormously, and it is worth knowing before you call anybody.

nothing at all. no lights, no click

a dead battery, or a connection to it. check the terminals: corrosion looks like white or blue-green powder, and a terminal that moves when you wiggle it is the fault.

a single loud click, lights stay on

usually the starter solenoid, sometimes a battery with just enough left to run the lights but not to turn the engine.

rapid clicking

almost always a low battery. there is enough current to pull the solenoid in, not enough to hold it, so it chatters.

it cranks, slowly, and will not catch

a weak battery, or on a very cold morning, oil too thick and a battery that would be fine in July.

it cranks normally but never fires

now it is fuel, spark or air rather than the battery, and the battery is innocent. a failed fuel pump, a crank sensor, a timing belt that has jumped or broken.

listen for the fuel pump priming for a second or two when you first turn the key to on, before cranking. silence there is a real clue.

it starts, runs for two seconds, and dies

often an immobiliser or security system fault: the engine starts and the computer shuts the fuel off because it has not recognised the key. try the spare key before anything else.

only when hot, or only when cold

temperature-dependent failures point at a specific sensor rather than a general problem, most often the crank position sensor when it happens hot.

what we would say about a boost

a boost gets you home. it does not tell you why the battery was flat, and if the answer is the alternator or a parasitic drain then it will be flat again tomorrow.

get the battery and the charging system tested afterwards rather than assuming the boost fixed anything.