Use a multimeter to test the wall plug. You should have 2 polls giving 110-120 volts each and a ground. It sounds like you may only have one side hot and the other not.
The thermal fuse is a safety device designed to protect the dryer from overheating. The fuse is located on the blower housing or at the dryer’s heat source such as the heating element on electric dryers or at the burner on gas models. The fuse should be closed for continuity meaning it has a continuous electrical path through it when good. If overheated the fuse will have no continuity meaning the electrical path is broken and the fuse has blown out. A multimeter can be used to test it for continuity. Be aware that a blown thermal fuse is an indication of a restricted exhaust vent from the dryer to the outside. Always check the dryer venting when replacing a blown thermal fuse.
To determine if the start switch is defective, attempt to start the dryer. If the dryer hums but does not start, the start switch is not at fault. If the dryer does not respond or make any noise, the start switch could be at fault. Use a multimeter to test the start switch for continuity. If the switch does not have continuity, replace it.
The door switch activates when the dryer door is closed. On most dryers, the door switch makes an audible clicking sound when it activates. To determine if the door switch is working, try starting your dryer and then listen for the “click.” If the door switch makes a clicking sound, it is probably not defective. If you don’t hear a click, use a multimeter to use the door switch for continuity. If the switch does not have continuity, replace it.