Dryer drum drive belt. 1/4 inch wide with 4 ribs and 3 grooves. The drive belt is a very long, slender belt that wraps all the way around the dryer drum, around a tension pulley, and then around the drive motor pulley. If the drum will not turn when the dryer is turned on the belt is likely broken.
Dryer thermal fuse. If the dryer overheats, the thermal fuse blows to cut off power to the dryer. If the thermal fuse has blown, the dryer won't start. The thermal fuse cannot be reset—if the fuse has blown, replace it. Thermal fuses often blow due to a clogged vent.
Dryer drum drive motor with pulley. If the dryer does not start the motor could be bad. Before replacing the motor the door switch and thermal fuse should be tested to determine if they are defective.