Troubleshooting falls into two categories: Grid failure or power failure. Excess dirt or a large object stuck in the grids will cause an electrical short. A loud snapping noise will sometimes indicate this problem. If cleaning does not stop the snapping and the grids are bone dry, inspect the fine wires stretched across the terminals. If they are white from oxidation, gently run an old soft toothbrush up and down them once, then rinse and dry again.
Most electronic air cleaners have a light to show operating power. If the light is not on when the system is running and the switch is on, there are two possibilities. The power pack has burned out, the power to it has been disconnected, or the unit has a pressure switch to sense air flow and charge the grids and it has failed. Either repair means opening up the power pack, exposing dangerously high voltage. This task should be left to a qualified technician.