This is a bad component inside the microwave. Usually a short circuited transformer or magnetron.
If you are well versed in electronics and electrical I can help you find the fault and replace the failed component.
But if not a word of serious caution here.
Microwaves can contain LETHAL voltages even when they are un hooked from their power supply!!!
So you really need to take precautions if you want to work on this one.
I will help you any way I can.
If you have the test equipment I can help you;-)
If not you will need to bring that one to a shop that fixes appliances or call a shop so they can send a service tech out to do this safely;-)
In any case, I will stick with you until this is complete.
Please rate my service kindly.
Also it is the only way I am credited for my time and expertise with you.
Once you rate, I will be notified and will add your question to my priority list so you can reach me anytime until this problem is solved.
Then you can reach me by simply replying to this message anytime.
Thank you and have a great Sunday!