could i suggest you try to diagnose the problem with a test light first before hitting the starter with a hammer. hitting the starter with a hammer could ,
1 free a solenoid,
2 free short brushes, or
3 even bridge a loose connection.
if it starts working you still don't know what is wrong.
short the two terminals marked red put a test light to a good earth and test if there is power at the blue terminal. if there is power and the starter is not turning there is a problem with the motor. if there is no power at the blue terminal fit a solenoid kit.