How to fix a exhaust fan in bathroom?

First, very important, you must stop the electricity. Go to your circuit breaker box. This is for your safety.

Then, take off the fan cover. It is maybe just very dirty inside. Use a vacuum to clean the dust from the fan and the motor. Clean the fan blades with a cloth. Sometimes, this is the only problem and it will work again.

With the power off, try to spin the fan blades with your finger. If they do not move, maybe the motor is broken. If the motor makes a big noise, it is also bad. It is often easier to replace the whole fan unit than just the motor.

If this does not work, maybe the problem is the switch on the wall. But if you are not sure, it is best to call an electrician. Be careful with electricity.