The answer to 'thermostat not turning on' is that there are several common causes, including a dead battery, faulty wiring, or a problem with the HVAC system itself. Symptoms may include the thermostat display being blank or unresponsive, and the HVAC system not turning on when expected.
Some potential solutions include replacing the thermostat batteries, checking the circuit breaker, and inspecting the wiring connections. However, if the issue persists or you're not comfortable troubleshooting the problem, it's best to call a professional HVAC technician to diagnose and repair the issue.