Diagnosis
A complete power loss indicates a tripped thermal fuse, a failed main control board, or no power from the outlet.
How to Fix It
Verify power at the outlet with another appliance. Unplug the microwave for 5 minutes. Plug it back in. Listen for a relay click. If still dead, check the 15-20 amp kitchen circuit breaker. Reset it by turning it fully OFF, then ON.
If That Didn't Work
The thermal cut-out fuse on the magnetron or cavity has likely blown. This is a non-resettable safety device. It requires component-level testing with a multimeter and replacement. A blown thermal fuse often points to an overheating issue.
Heads Up
If the microwave was recently installed, confirm it is not plugged into a switched outlet controlled by a wall switch. A blown thermal fuse is a symptom, not a root cause. The overheating issue must also be addressed.