I went to start up the car and it is turning over but will not start. What could the problem possibly be?

Possible starter failure if the engine doesn't crank. You can try tapping on the starter motor using a blunt object while turning the key to see if it starts. If it starts, suspect a defective starter motor. If it is a manual transmission, you can push start it in gear

It's possible, but then you have the possibility of it being sucked into the oil pump if the pick-up screen is damaged or missing.

My guess is that your A/C went out. Either your compressor went bad or possibly a coolant leak. An easy way to check if it's the compressor is to start your car and lift the hood. When you turn the A/C on you should see the compressor clutch engage. All that means is that the piece in front starts turning as well. Otherwise your best bet is to have a mechanic look at it. Hope this helps!

It will turn over but will not start.It can be battery, starter or fuel issue.As it started this problem after shifting to gear, but did not shifted , it can be transmission related issue.But most probably its battery and other possibilities casing the problem.Click the link below for more troubleshooting:---

http://technoanswers.blogspot.com/2011/05/car-will-turn-over-but-will-not-start.html

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This should help.Thanks.Helpmech.

Check the other ends of the battery cables for cleanliness and tightness. If they are solid, it's possible that although you replaced the battery terminals, the battery has a bad cell and needs replacement. If the car starts when it's cold and won't start when it's warm, the problem could be a bad starter. A bad starter will function properly when cold but once warm, requires much more power to turn over.

dealer only the immobilisor has cut in when the battery went dead ,its also possible the ECU was damaged by brown out when the battery went flat .

First check with locale Pontiac dealer giving your full vin number of car to determine if it has anti-theit. feature. If so, there is a chip in key to allow it to start. May require a new chip key cut from vin if chip went bad if that is at all possible. Never heard of a chip going bad but anything is possible.

Very possible you may have a faulty voltage regulator. I would have it tested which many places do for free.

Check your fuel pump for possible dirt or blockage.

could possibly be a flat battery possible could be the starter motor also when you unlock the car with the key the immobilizer should of disarm