The answer to 'my humidifier won't turn on' is that there are several common causes, including a faulty power supply, a clogged filter, or a problem with the humidistat control. Symptoms may include the unit not powering on at all, or the humidifier running but not producing any mist.
Some simple troubleshooting steps you can try are checking the power source, inspecting and cleaning the filter, and verifying the humidistat is set properly. However, if these basic fixes don't resolve the issue, it's best to call in a professional HVAC technician to diagnose and repair the problem, as there may be more complex electrical or mechanical issues involved.