Car turns over but does not start.

didnt specify year -generic answer -watching to many movies cant hot wire coils,ignition vehicle etc --if starting and then stalling your getting spark and fuel need to look into sensors -fuel pump relays ignition system

Possible bad crankshaft positioning sensor?

Does the check engine light come on? if yes
Could be faulty crankshaft sensor

This problem usually doesn't show up on diagnostic, it is a problem that saturn has with many of it's cars, it is either the ignition module or the crank sensor, I think replacing the crank sensor would be your best bet, that is what was wrong with mine and I didn't find that out until I replaced the fuel filter, the fuel pump, the ignition module and the coils, trust me, go with the crank sensor.

If it turns over but won't run, I would check to make sure you're getting fuel and spark. Pull a plug after turning the engine over a few times and if it smells like gas then you're getting fuel, if not then that's your problem. If you're getting fuel, you may not be getting spark. Hold the plug against the engine block and have someone turn the engine over a couple times. You should be able to see spark, but if not then there's your problem. Good luck!

i need more information like is the car rolling if it is first thing you need to chaek is if its getting spark take the number one sprkplug out and place it on a good ground on the engien and have someone roll it over if its not getting spark then it could be the coil . but if its getting spark than it might mean its not getting gas

i would have to say first check the fuel injectors fuse in the under hood fuse block if blown replace it,sometimes the fuel injector harness rubs thru anywhere from where the harness comes thru the firewall all the way up to the injectors,,,if fuse is good and no bare wires to injectors,check the wires to the ignition module,,,,and if all checks ok,i would replce the ignition module,,you could have spark from it but it could not be sending the signal back to the pcm to fire the injectors,,,and if all that fails try a pcm,but i think youll find it before that,,i seen this 3 times and each time it was a wire rubbed thru near the fuel rail and it grounds out and blows the injector fuse,
hope this helped

check timing belt!! good luck!!

It could be, and almost definitely is very possible its the brain ( ECU or Electronic control module) Will all the things you said it is doing that is probably the problem. Caution : Computer problems are EXPENSIVE

fuel, oxygen, and spark. Check all of these. Is it getting air. Is your filter clean. Are you getting spark. if not check your plugs wires and coil. finaly check your fuel. Are you getting enough fuel. Replace the filter, make sure you are getting enough psi's before the injectors. also make sure the fuel pump is working.

You will probably need to put your car on a computer scanner.

Let me know what you find.