Swapped 2003 Pontiac Grand Prix GT engine into 2002 and it wont turn over.

Tom is right! I would certainly check all battery and possible starter problems -- I'm assuming if you were able to swap motors you are checking that stuff over again. Also you need to know if the motor moves at all. Can you turn the motor by hand? Meaning-- can you put a socket on the crank bolt and spin the motor? If not then you have a mechanical and not electrical issue. One common mistake (which I have done!) is not to get the torque Convertor pressed completely in and it binds up the flexplate so your starter cant turn the motor -- so post some more details and we ll see if we can help!!

could be almost anything, you say you crashed the car the engine came out of, so it could be an endless list of things. dis the engine get damaged in the wreck, electrical problem, torque converter binding m, bad starter, no ground strap, just to mention a few