Check the electrical outlet for power. Reset the house circuit breaker if the electrical outlet is dead.
If the electrical outlet works, shut off the compressor and bleed all the air from the tank. Flip the pressure switch control lever to the Auto position. If the pump starts when the tank is empty, then the check valve may be stuck open. The check valve prevents tank air from back flowing to the pump. A stuck-open check valve causes high pump head pressure, preventing the compressor from restarting.
To test the check valve, let the air compressor fill the tank until the pump shuts off. The pull the ring on the safety valve to bleed air from the tank to reach the cut-in pressure, so the pressure switch tires to restart the motor to refill the air tank.
If the compressor won't start with air in tank, replace the check valve.
If the compressor won't start with an empty air tank, replace the pressure switch if it isn't activating the pump motor.
Replace the pump motor if it doesn't start when activated by the pressure switch.