Dryer cycle ends digital timer goes to zero but dryer keeps running.
You will either have a wiring issue in which there may be an exposed wire or the control board WE4M488 for your unit is faulty and not cutting the motor circuit.
Dryer started turning off on its own and you could manualy restart but, now doesn't turn on at all.
With the dryer not turning on, you will want to check the door switch for continuity. It sounds like the switch may be defective and causing intermittent shut of but finally went out and causing the unit to not operate at all.