These run very small motors with low "starting torque" If the fan hasn't been run for a long time, its possible that it has jammed up or got tight from just sitting there. Being careful, turn on the fan and spin it in its usual direction by hand, it should start running. If you cannot spin by hand, it may have seized up which will require you to strip and lube the motor. If you manage to get the fan spinning , let it run on high fan speed for an hour or so, it should free up and then be OK again. A small spray of WD40, CRC or similar spray can lube on the fan shaft where it disappears into the motor may assist.