When you push the start button on your dryer and you hear a humming sound coming from the motor area, it is not time to panic, yet. Yes it could be a defected motor but it is possible that the motor centrifugal switch is hung up. A dryer centrifugal switch uses centrifugal force to open and close contacts on most dryer motors. When a dryer motor comes up to speed, weights on the dryer motor slide outwards taking pressure off the plunger on the centrifugal switch. This allows the switch to open contacts to the start windings and close the heavy duty contacts for the dryer heater.
Hold the start button long enough and you will burn up the run windings. Another big problem with dust causing the centrifugal switch to be hung up is that the contacts to the dryer heater are closed.
Maybe you will get lucky and have a louvered access panel on the back of the dryer right behind the motor that can be removed.
Switch back to regular vacuum and clean up all the lint in the dryer base area. Use your fingers to slide the weights back and forth on the dryer shaft making sure you do not knock off the springs. DO NOT lubricate this area as this will only attract more dust.