Diagnosis
No power to the control board. This is usually a blown thermal fuse or a failed door switch, not the start button itself.
How to Fix It
Check the thermal fuse first. It's a small, cylindrical fuse located on the blower housing or heater assembly. Unplug the dryer, disconnect its wires, and test for continuity with a multimeter. If it's blown (no continuity), replace it. This is the most common cause of total death.
If That Didn't Work
Test the door switch for continuity when the door is closed. Also check your household circuit breaker or GFCI outlet—dryers are often on a dedicated circuit that can trip.
Heads Up
A blown thermal fuse is a symptom. Before replacing it, you must find and fix the root cause, which is almost always a clogged vent system causing overheating.