GE SpaceSaver Microwave Suddenly Went Dead

GE SpaceSaver over range microwave suddenly went dead after running for 25 minutes. Light went out, turntable stopped, power vent froze, and all heating ceased. Home circuit breaker panel checked on. I’m thinking this failure must be power related. Unfortunately, the cabinet maker/home builder installed the unit without any access above the microwave. No cabinet doors, no screws to remove a panel, no access whatsoever. The whole thing is nailed together. Looks like I’m going to have to somehow cut a rectangular hole into the cabinet panel above the microwave, maybe 2 inches above to clear the cabinet frame. The hole would have to be around 4 inches high in order to get my hands in. That’s the only way I can think of to get access to the three mounting screws that hold up the microwave. Then perhaps I’ll have to seek a cabinet maker to construct a decorative wood plug to fill the hole. I’m open to any suggestions on repair and access. Thank you!