I can hear the motor on the fan it starts to turn but won't

Often when the fan buzzes but doesn't start and then starts when you give it a nudge and/or it starts only when switched to hi speed , suspect the starting capacitor. If the fan doesn't start at all , use an ordinary ohmmeter to check continuity at the plug end while switched to different speed settings. If there is a reading check to see if the reading changes slightly when switching between different speeds. If readings are obtained it indicates that the coil wires are ok. If no reading at all then suspect the small thermal fuse is open (because it did it’s job) protecting the motor from overheating and burning out the coils. This can be caused by a u/s cap or as mentioned in other answers , by lubricants having become so sticky that the starting torque is just not enough to turn the motor which will cause it to overheat and open the thermal fuse. The latter can be replaced with some difficulty and a steady hand. It is normally heat-shrunk and soldered between a mains wire and a thin enamelled copper coil wire.

Try to jump start your fan by pushing it with your hands after starting it. If that doesn't work, then check the fan's wiring- find an electrician, or call the fan's company and check if you still have warranty.