According to PartSelect, dryers typically do not start due to technical or mechanical difficulty. The site notes that problems are easy to diagnose and it is easy to order replacement parts if necessary.
PartSelect points out that one problem may be the dryer's door switch. Modern dryers do not start tumbling until the door is closed, and a defective switch may keep the dryer from detecting that the door is already closed. Locate the switch that is typically behind the front panel, and test it with a multitester to measure continuity.
PartSelect explains that the thermal fuse may also keep the dryer from starting. This fuse is designed to keep the dryer from overheating, and a malfunctioning fuse may keep the dryer from operating. Use the multitester to measure continuity on the starter switch inside the dryer, replacing parts as needed.
PartSelect recommends finding a qualified person to see if the motor in the dryer is defective and to replace it if necessary. The technician should examine the dryer's main control board to ensure that it is not malfunctioning. According to PartSelect, the dryer's timer should also be checked for malfunction because a malfunctioning timer can prevent the motor from getting power and prevent the dryer from starting.