The magnetron is most likely gone. Before replacing it make sure that the wave guide (place where the magnetron antenna goes in) is not damaged.
The magnetron Part number: W10126786
Here are the breakdown diagrams and Replacement parts for Maytag MMV4205BAW MWAVE- MOUNTED OVER RANGE/WO | AppliancePartsPros.com
Best if you can post the picture of the oval opening.