The fuse inside the microwave is for all power to the microwave. The MW will be completely dead. Sounds as though the magnetron or start capacitor is bad. Cost for replacement mag, if you can find one, will cost as much a new MW. It is possible that a wire came loose on the capacitor or Magnetron. I worked on thse for years and 90% of the time it was the Magnetron.Nearly all microwave ovens have an internal fuse that is by far the most common thing to fail. If you are bold enough to look inside, it isn't usually that difficult to replace.