Some reasons the compressor will not start and man, is that aggravating.
Here are a few of the things you need to look at when your air compressor just will not start.
Plug in? OK, your next check is....
Can you get to the electrical service / power panel in your garage or house? Have a look inside it and see if any of the breakers are tripped, or fuses are blown. If so, reset the breaker or change the fuse.
Or, plug a trouble lamp into the same socket that the air compressor will be plugged into, to make sure that there is power at the socket.
You will now have identified for sure that the air compressor is the source of the electrical problem, and if the breaker or fuse lets go when the compressor tries to start, you have an electrical problem at the compressor that might be caused by a bum pressure switch, a start capacitor has failed, the motor is failing or overloaded... there are a host of reasons, covered on the Troubleshooting pages.
Is There Pressure?
Next check...look at the gauge on the compressor tank. Is it showing pressure? Is that pressure reading higher than the high pressure cut-out of that compressor? If you are not sure, leave the unit plugged in and either bleed air from the tank through the air tool or (I suggest you wear a work glove) reach under the tank and open the tank drain valve and let the tank completely empty.With the air tank empty, the danged compressor still will not start?
If not, and assuming you have got electrical power flowing to the pressure switch, by plugging it in with the tank at zero pressure, you should hear a click as the pressure switch trips due to low pressure. It should trip and send power to the electric motor.
Can you check? If you have a multimeter, you can check to be sure that power is actually flowing to the motor. And, if you have a multimeter, you don't have to kneel down and listen, just dump the air, plug in or start the compressor, and see if power is flowing through the switch.
If the motor does not start at this point, and it is getting power, what is the motor trying to do?
If the compressor motor starts, this suggests that it went out on thermal overload, and you may have an overload or motor overheating problem.
To check, when the tank pressure gets up to the cut out level, and the compressor stops, bleed the pressure down again, and monitor the start sequence. If it restarts, well, just carry on. If the motor balks at starting again, it may be the start capacitor or the motor itself that is causing the problem. Or...
Also, monitor the unloader valve when the compressor cuts out to make sure it is working. If the unloader valve does not operate, that is a good reason why your compressor will not start the next time the pressure switch sends power to the compressor motor.
Hope these tips are helpful. And, of course, if you still need help, just ask.