The dryer runs but only if you hold the start know down.
The dryer only running when pushing on the start switch would be caused by a bad centrifugal switch on the motor and the motor WE17M37 would need to be replaced.
I have a GE dryer. The dryer will not start, I checked the timer knob and found that the plastic is cracked where it slides on to the shaft. Could the be the cause ?
It is possible that the timer knob being cracked would cause the timer to not be in the correct position to turn on. You will want to replace the timer knob but you also want to make sure that when in the correct position that the dryer comes on and if not check the door switch and thermal fuse for being bad.