The answer to 'switch not working' is that there are several common causes, including a tripped circuit breaker, a faulty switch, loose wiring, or a problem with the electrical box. Symptoms may include the switch not turning on the light or appliance, the switch feeling loose, or no power going to the switch.
To troubleshoot, first check the circuit breaker to ensure it hasn't tripped. If the breaker is fine, use a voltage tester to check for power at the switch. If there's no power, the issue may be with the wiring or the switch itself. Replacing the switch is a relatively simple DIY repair, but if you're not comfortable working with electricity, it's best to call a licensed electrician.