Inspect the wiring extending from the box. Make sure that one wire attaches to ground. Another wire should connect to the pressure switch. Also verify that the power wire connects securely into the main circuit breaker panel.
Replace any of the electrical control boxes' internal fuse has blown. If the fuse is not blown, make sure it is the manufacturer recommended fuse size and value.
Open the electrical control box with a screwdriver. Visually inspect the printed circuit board. Make sure that the starting capacitor has not blown. A blown component will be obvious on the PCB by a charred spot on the board and an intensely bad smell.
Test the incoming positive and negative electrical leads for voltage. Connect a multimeter's negative lead to the boxes' ground wire. Attach the multimeter's positive lead to the wire supplying electricity from the main circuit breaker panel to the control box. If no voltage reading displays on the multimeter's display, the electrical control box is not receiving any power. Check the circuit breaker panel for a tripped breaker.