One way to fix an oscillating fan is to tighten or replace the gears in the gear assembly. Replacing the blades is an option if the fan has shaky blades, but another alternative is to affix washers to the blades for proper balance.
Replacing the gears may be necessary when the fan head doesn't turn properly. To access the gear assembly, unplug the fan, and pull away the fan grill to reach the motor casing. Remove the screws and clutch knob of the casing to see the gear assembly. If the gears aren't the problem, check the internal assembly motor for any dust or debris inside. If the motor is dirty, use a vacuum to clean it by placing the suction on the grill to suck out dirt from the housing and motor. Unplug the fan, and remove the grill to see if the blades are also plagued with debris.
Check the adjustment knob to see if it is jammed, which can cause the motor housing to stop functioning. Pull the stuck knob, and push it back down firmly but gently. The button is connected to the motor housing.
The fan may also not operate if the cord becomes loose. If the fan is plugged into a power strip, the plugging and unplugging of other cords can dislodge the fan cord from the outlet. The weight of the cord itself may also cause it to disengage from the outlet.