Can I assume it’s just a fan (no light bulbs)?
Although it could be the motor, my first guess would be the switch. Either way, you’ll need to take it down. (You’ll want to flick the breaker before you do.) When you detach the fan from what ever is holding it up you’ll need to undo the connectors (plastic cone-shaped things that screw on and off the wire connections – usually red). If you remove the connectors and find separated wires, then there’s your problem.
But somehow I don’t think you’ll find that.
If there’s an easy way to inspect the switch, I’d do that first. Maybe something’s gotten it jammed up. When you pull the cord, does it feel/sound right? MAYBE you’ll be able to un-jam the switch. MAYBE, if you’re handy, you’ll be able to find a replacement switch at Home Depot and install it w/in the fan. I fixed a few desk lamps this way.
If it’s the motor, or you just can’t tell, then there’s little you can do that won’t cost more than a new fan. Unless you know someone who’s good at fixing electrical things.
Anyway, just my $.02.