Some of the most common issues when dryer will not run are:
Incorrect voltage at the dryer.
Door switch having bad continuity on the switch contacts.
Bad continuity of the motor windings or grounded motor.
Timer having bad continuity of its switch contacts.
Bad “push to start” switch for continuity of the switch contacts.
Broken or loose wiring. Wire terminal connections that connect to the different components.
For electronic control models with electronic control board normalcy you would see an error code, which you can google.
Remember safety always your priority and always use professional and trained appliance repair technicians when dealing with electrical or gas appliance repairs !