The overheat sensor has done its job and shut down the controller. The fans should still run. Let the welder cool off for a few minutes and it should weld again. The welder worked beautifully, but after welding for two hours solid, something smells funny and you either get no arc or only full amperage. You have fried the SCR module and overheated the transformers.
Most welders have a duty cycle.
A duty cycle hasn't been determined for this arc welder. It actually varies depending on how high an amperage you are welding with. And remember to keep the air vents open and to keep the insides of the welder free of dust build up. Dust acts as insulation and hinders proper cooling. Another thing to do to help the welder stay cool is to hit the fan only switch between welds.