The answer to 'why is my ductwork not turning on' is that there could be several common causes, such as a tripped circuit breaker, a faulty thermostat, or issues with the ductwork itself. Your ductwork may not be turning on if the power supply to the system has been interrupted, the thermostat is not properly controlling the system, or there are blockages or leaks in the ductwork.
If your ductwork is not turning on, the first thing to check is the circuit breaker or fuse that powers the HVAC system. Make sure it has not been tripped or blown. Next, inspect the thermostat to ensure it is set to the correct mode and temperature. If the thermostat appears to be functioning properly, the issue may be with the ductwork itself, such as a blockage or a leak that is preventing airflow. In this case, it's best to call a professional HVAC technician to diagnose and repair the problem.