1) remove the spark plug & try again. If it spins freely then you had a hydraulic lock ( fuel fitting up the cylinder ) or your valve lash is too big
If not then
2)Try ( briefly ) hot wiring the starter directly to the battery . good then you have a solenoid/ control wireing problem- earthing problem.
No joy then it's a starter motor problem
3) try again with the + wire removed if good then you have an earth problem.
