Unplug or disconnect power to the machine and access the electronic control board. Remove the screws in the back of the top panel, then lift the back of the top panel and slide back to remove.
The electronic control board is located on the left side near the top. It's very common for that part to fail. Look on the back side for a burned or scorched mark near the relays.
Measure the resistance between P1-3 and P1-4. If the resistance is between 1-6 ohms, replace the control board. If not check the belt switch for continuity.
Check the motor windings at the motor switch. Disconnect the motor connector. Measure the run/main windings between the blue wire in back and the white/orange wire (2.4-3.6 Ohms). Measure the start windings between the blue wire in back and the Violette wire (2.4-3.8 Ohms).
Lift the idler pulley up and measure between the two blue wires to check the belt switch.
I wanted to thank you for this post as it enabled me to get started on my own repairs of the same problem. I also wanted to add a couple of comments. First when I originally did the P1-3 to P1-4 test, I tested out at infinite ohms and because that was not in the 1 - 6 ohm range I assumed I was OK and went on. I then ohmed out the motor and the belt switch and those were both fine, so I started going through the wiring diagram when it dawned on me that it mattered in the p1-3 to p1-4 ohm test that the door had to be closed in order to get a proper reading. So first comment is the manual might say make sure the door is closed. Once I closed the door I had a reading of 2.4 ohms so I was pretty sure the control board was bad, so I removed it to see if I could see any burn marks etc. from a burned out motor relay. This is when I got lucky. What I found instead was a bad solder (almost missing) joint on the board right at the relay where it goes over to the motor. A quick resolder job and of course putting my machine back together and I was back in business with no cost other than my own labor. Prior to checking the motor control board I had already checked the thermal fuse and dampness sensor and knew they were working. Thanks Jake for an excellent thread. I bet you have helped allot of people fix their dryer.