It is possible that the fan overheated and there is an automatic shut off. Give it a try in a few hours and see if it starts again. If not, then I would say the fan is shot. I have replaced our bathroom fan twice in 16 years.
Sometimes, if the blades connected to the motor are not cleaned for a long time, they accumulate heavy dust and debris (for the size of the motor), and this will cause the motor to overheat and kick off. If you take the plastic grill off...you should be able to see the plastic little blower fan blades. If they're clean, make sure the motor didn't become unplugged also. It plugs into an outlet in the ceiling box. MAKE SURE THE SWITCH IS OFF WHILE YOU TOUCH ANY PLUG. The other possibility besides the motor being defective would be that the plug the motor plugs into does not have 125 volts (electrician at this point?) Good luck.
Before touching any electrical wiring, turn off the breaker, not the switch.
I have seen, more than once, the neutral wired through the switch instead of the hot. This left the hot in the ceiling live even when the switch was off. Never depend on a light switch, play it safe and shut off the breaker!
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