Otto, start with the basics. Pull the lint screen housing and clean it out, pull the back of the dryer and clean it. Make sure that the exhaust pipe from inside the dryer is clean, and that the vent to the wall is clear as well. If that checks out okay, try to run the dryer for a short time with the door open. Depress the switch, that is normally closed by the lid, and feel if there is any hot air. It is possible that either your thermal fuse has failed, or your heating elements. Get the service manual from here and check the wiring accordingly.