My xa blew the head gasket at over 170k last week so I decided to swap in a low mileage motor instead of doing a rebuild. After getting it into the car and ready to rock, it won't turn over.
The starter just clicks. We pulled the starter and it still spins it just won't spin the engine. It is the starter from my original engine and worked fin before the swap. We cleaned all the electrical connections and tried the ol 'smash on it with a hammer' technique but nothing is working. Any ideas on what the problem could be?

 

Did you use any other parts from your previous engine? Also, check if you can manually turn the engine, put the car in neutral and turn it at the crankshaft bolt clockwise (someone check me on that). If you can't turn the engine then something mechanical may be busted.

You can also try following this guy's procedure.