Why would bathroom exhaust fan stop working? No sound at all from fan. No problem with anything else.

You may be able to remove the grill, unplug fan, then plug in a lamp or tester to see if it is the fan or lack of power.

If you remove the exterior grill you will see most exhaust fans actually have short pigtails and plug into a single outlet in the unit. Unplug it and test for power. If you have power then replace the blower unit. Fans like Broan and many others a single screw allows you to drop the plate with the motor and buy a replacement