Hi. Welcome to JustAnswer.If the answer I provide for you is helpful, please click 'ACCEPT'. I won't be paid if you don't. Most likely the magnetron has failed. Unfortunately that part is no longer available.
I am sorry, but your best solution is to consider purchasing a new unit.
Please let me know if you require further assistance, or information. If not, please click on "ACCEPT". After you accept, please leave feedback.Thank you.