Microwave had worked perfect and last week everything dead. checked 50 amp breaker and was still on.

Shut off breaker and tried to reset. nothing

Shut off breaker and took side and top off microwave and fuse as well top portion of fuse holder was blown and melted. ordered both these parts as well new bulb. Waiting for delivery. I had a copier - large Xerox I was working on in the garage and did not know if it was possible that it shorted had a power surge that impacted microwave. Otherwise I am trying to figure why microwave may have shorted before replacing fuse? Any thoughts. Main board? Anything else I can check before firing it back up with new fuse and holder?
Thanks