Hi Andy, Welcome to the forum
Re' your query, your question is a bit broad, we need to know what if any is on the control circuit, what test results are for the control circuit, I assume you have checked the O/L unit hasn't tripped and needed resetting too.
It should be pretty easy to identify the issue here but other than a faulty start contact block I would edge my bets your stop circuit is open circuit or loss of power to control, if this is due to the O/L been in a tripped status then pushing the main contactor in manually is not a good idea as you could damage the motor.