Look over the electrical cord and make sure it does not have any breaks or frays. Look for any black marks along the cord. This is a sign that the cord has frayed on the inside and the wires are crossed. The black marks are actually burns on the inside of the cord.
Replace the power cord if you find any cracks, breaks, frays or burn marks on the exterior. This will not only inhibit your unit from turning on, it will also put your shop at risk for an electrical fire.
Plug the unit in with a new electrical cord and allow the fan to run on the unit. If you have been using the welder for awhile, the thermostat might detect heat on the system. When the unit gets too hot, the thermostat will cut it off and allow it to cool.
Turn your unit on after the thermostat has cooled. If the unit still won’t come on, you need to take it to a service shop to have it looked at by a professional.