In short, you should not try to fix your noisy air conditioner on your own! Unless you have professional knowledge of HVAC electrical system layouts and the proper meters to test all the working components of your AC, you are putting you and your air conditioner at a significant risk for harm.
The humming could be a couple of different things, such as a turned off breaker at the panel box or a blown high voltage fuse at your outdoor disconnect box. Another (very likely) possibility is that the humming sound is due to a bad start capacitor for both the compressor and the condenser fan motor.
The capacitor’s job is to provide a boost of energy to both the components at start-up, so when the capacitor fails, the fan motor will not run and the compressor will try to start for a few seconds and hum very loudly—resulting in a very noisy air conditioner! It’s incredibly important to have a trained professional diagnose the humming sound coming from your air conditioner before the problem gets worse.