replaced radiator in a 2008 chevy cobalt lt 2.2l due to leak and over heating. had trouble with trans coolant lines leaking that attach to radiator because was missing little plastic rings on line fittings that attach to radiator. got rings from old radiator and was leaking a little bit after messing with for a while. filled with water and started car and ran a bit then shut off and drained radiator to flush. repeated process car temp got to 244 shut off let set a while drained and then added coolant and water mixture. replaced bumper and headlights. now cannot get the car to start and is now leaking from back of engine. hard to see where coolant is coming from but possibly from water pump but not sure if coming from above pump. drips all the way down and off of transmission. car is turning but not starting. radiator holds some water and drip stops but coolant leaks when i add more and worse when i try to crank it over. hope its not the head gasket or related? was never white smoke and dipstick oil looks clean. what could be the problem?