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If the microwave isn't heating but it sounds and looks like it's running, it means that your magnetron has overheated and failed. There is a thermal cut out on the microwave which cuts power to the entire microwave if the magnetron gets too hot and that is why the display went blank and nothing worked until the magnetron cooled down. Unfortunately at this point the magnetron would need to be replaced to resolve the issue which is about $150 typically for the part depending on the exact model number, and another $150 to replace the part.
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