Dryer knob sticks in one spot- won't move

 Door switch / Door switch actuator leverThe dryer would not start with a broken door switch. Replace the door switch if found defective.

Most dryers have a door switch actuator lever - when you close a dryer door, it presses against the lever, which actuates the door switch. If the lever is broken, the switch would not activate and the dryer would not start. Replace the lever, if broken.

Note: Door switch actuator lever usually comes with the door switch assembly and it is recommended to get the whole assembly since there is almost no price difference between the door switch assembly and just the lever. Check your model for more details.