2004 ion won't start. Lights work. When I turn key don't get series of clicks, get one snap.

use test light, connect clip on grnd. , touch tip on the starter wire while turning key , if it lights starter is faulty , no light, solenoid is faulty, if it lights and indicates starter is cause you can try to gently tap starter with plastic handle of screwdriver if tapping gets it moving then brushes in starter are dirty or near worn out hope this helps

I would suspect the fuel pump is the problem, it may be sticking at times and this causes a no start. The pump is located inside the fuel tank and it is electric.

Try using the second key if you have one. Does the key not working look like it is bent? The ignition cylinder may just be worn to the point that it needs to be replaced.

Not sure, but I've heard a bad hazard switch can cause strange problems.
Also, if your truck has a body control module that controls interior and lights, that may be your problem, too. Good luck.

more then likely its a bad starter. or the cable to starter.

If you haven't replaced the fuel filter in the last year or so, do it now-basic maintenance.
Check if the pump is working by turning key to ON (not crank), and listen for the pump in the tank to come on for a couple of seconds. Should hear a short hum or buzz verifying tank is working. If you don't hear it come on, either the pump is bad, or power is not reaching it. May have to pull the pump connector off at tank, and check for 12 volts on pump wire when someone cranks the car. If power there, the pump must be bad. If no power there at pump, check fuses for pump and fuel pump relay.

battery dead.

blow horn, see if lights in dash light up then turn key all the way like you start car if lights go out and no engine clicks are anything u hhave starter probelms replace it

I would check your battery. I would also look for loose grounds. The clicking you hear is your fuel pump turning on. I would check your battery voltage and, have the battery load tested.

You need a new starter solenoid. It is essentially a heavy duty remote switch that is activated by your ignition key switch. The solenoids get stuck or don't conduct well after 6 to10 years.