1. Make sure the main power knob is ON as well as the inverter. The purple inverter controller, if it's on, should show a voltage reading.
2. Make sure the compressor switch on the dashboard is in the UP position
3. Make sure the mast control switch is set to "RAISE"
4. Drain all the air out of the compressor tanks manually by opening the valve on the bottom tank. Twist the valve slowly to release the air. If a lot of water also comes out, it's possible the water was interfering with the pressure instead the compressor and now with it all drained, the compressor should turn on.
5. If that still doesn't work, try plugging the compressor directly into shore power instead of the inverter. If that works, the issue could be the compressor is trying to draw too much voltage and the inverter is not allowing it. Try plugging the compressor back into the inverter and see if it will turn on now that it had been unplugged from the inverter. If the compressor will not work when plugged back into the inverter, then the compressor needs to be replaced.