The answer to 'my tune-up won't turn on' is that there could be several common causes, such as a tripped circuit breaker, a faulty thermostat, or issues with the electrical connections. If your tune-up isn't turning on, the first thing to check is the circuit breaker to ensure it hasn't been tripped. If the breaker is fine, you'll want to inspect the thermostat to make sure it's set properly and functioning correctly.
If the thermostat seems to be working but the tune-up still won't turn on, the issue may be with the electrical connections or other internal components. This is where it's best to call in a professional HVAC technician, as diagnosing and repairing electrical problems often requires specialized knowledge and tools.