How old is this fan? Is it very dirty? Often spinning blade fans collect LOTS of dust, and when that dust gets inside the motor housing it can gum up the works and cause problems like you describe (though there are other causes too). [br]
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First recommendation would be to disconnect from power, remove all the housing screws to take off the housing and carefully clean and inspect the motor and other internal components. There's a chance a good cleaning will get it working again, or at least reveal something like a blown capacitor or other failed component that could be replaced to get it working again.