The answer to 'my circuit breaker won't turn on' is that there could be several common causes, including a tripped breaker, an overloaded circuit, a short circuit, or a faulty breaker. The symptoms may include lights or appliances not working, and the breaker refusing to stay in the 'on' position.
To troubleshoot, first check the circuit breaker panel to see if the breaker has tripped. If so, try resetting it by switching it all the way off and then back on. If it immediately trips again, there is likely an issue with the circuit that needs to be addressed. This could be an overloaded circuit, a short circuit, or a problem with the breaker itself. Attempting to reset a repeatedly tripping breaker without identifying and fixing the underlying cause can be dangerous and may result in further damage.