The answer to 'my humidifier won't turn on' is that there could be several common causes, such as a faulty humidistat, a problem with the power supply, or a mechanical issue with the humidifier itself. The symptoms you may notice include no power to the unit, the humidifier not cycling on and off as expected, or the humidistat not registering the correct humidity levels.
For simple troubleshooting, you can start by checking the power supply and ensuring the humidistat is set properly. If those don't resolve the issue, you may need to call in a professional HVAC technician to diagnose and repair the humidifier. Attempting to disassemble or repair a humidifier without proper training can be dangerous, so it's generally best to have a qualified technician handle any major repairs.