The answer to 'my AC won't turn on' is that there could be several common causes, such as a tripped circuit breaker, a faulty thermostat, or a problem with the compressor or other components. The symptoms may include the fan not running, the unit not cooling, or no power to the system at all.
To troubleshoot, first check the circuit breaker and reset it if tripped. Next, check the thermostat settings and replace the batteries if needed. If those don't resolve the issue, you may have a more complex problem that requires a professional HVAC technician to diagnose and repair, such as a refrigerant leak, a faulty compressor, or an electrical issue.