car is going crazy

Ok I have a 2000 hyundai elantra. It took it along to crank it up then acted like it was flooding itself out. The engine sounds different then usual when I try to crank it, and there's a puff a white smoke that comes out, but i think thats due to it taking so long to crank. Does this have something to do with the fuel and air flow. The check engine light came on so I am sure that a sensor has went dead but I am not sure. Can anyone please help me with this?????

puff of white smoke usually comes due to a blown head gasket. white smoke generates due to the burning of a coolant in an combastion chamber.