Thank you for using Just Answer!
The kind of failure could be due to failure of the magnetron tube, the power relay that supplies the magnetron tube, or the high voltage supply for the magnetron, especially if the turntable, fan, light and controls all still appear to be working. The high voltage transformer is the most likely to have failed. This transformer has both high voltage and low voltage capacity so it is possible for the high voltage windings to fail yet the low voltage windings still supply power to the controls. Another possibility is the rectifier used in the DC supply for the magnetron.
Ultimately there is some type of high voltage problem with the microwave. Whether it is the high voltage transformer, capacitor, rectifier or magnetron you should never try to self-diagnose or work inside a microwave unless you are a trained technician.
Microwaves carry high voltages, even when unplugged, and can result in serious electric shock and death. I stress to call a certified technician to diagnose the problem and provide with a cost valuation to help in your decision to either repair or replace.
A thermal fuse failure is a possibility. The door latches also have been known to fail and result in the microwave not heating. The fuse replacement would obviously be the most affordable repair, but you are still going to need to pay a technician to visit your home and diagnose the problem. Depending upon what the service call fee is will also have to be factored into the repair or replace decision.
I recommend calling a couple repair companies in your area and give them the model number and ask them what a service call fee would be. If the service call fee is substantial then you may choose just to forego and buy new. Anything other than a fuse replacement is probably not going to be cost effective as a repair option.
Good luck with your microwave. Please feel free to follow-up with any additional questions. Positive feedback is much appreciated!!