First, is the motor turning or not, if the answer is yes, the main gear may be worn out at his center point where a small shaft hold it. When this happens, the main gear becomes off center and the motor gear system is just away from the main gear, in other words, they don't come in contact, so the motor just spin freely. Easy to check, just remove the handle by removing the screws, the gard one screw at the blade section,, remove the 4 bolts that hold the blade system, you will see the gears at this point, and if they are away from each others, you will be able to move the main gear side to side if it is the case. just turn the unit upside down, and the main gear will fall in your hand. Check it out.