The answer to 'my air conditioner won't turn on' is that there could be several common causes, including a tripped circuit breaker, a faulty thermostat, or a problem with the AC unit itself. The symptoms you may experience include the unit not powering on, no air blowing, or the fan not running.
Before calling a professional, you can try some basic troubleshooting steps. First, check the circuit breaker and reset it if it has tripped. Next, check the thermostat to ensure it is set to 'cool' and the temperature is set lower than the current room temperature. If those don't resolve the issue, it's likely time to call an HVAC technician to diagnose and repair the problem.