Air conditioning condensing unit won't come on.. . there is a humming nosie so I know it's got power.

Have you checked the high voltage? The breaker first,, then check for 230 volts at the contactor,, while you are in there look at the capicitor,, is it swollen,, does the top look like a frozen coke can all pooched up and looking overfilled,

, check these items and let us know

The humming you are hearing is probably the contactor pulled in and low voltage does that, (24 Volts)