Is my microwave over and done with?

Most likely it's done for. Try again -- double check all your settings and try to heat up a cup of water. Alas, they're typically not worth repairing, and if you're sure you haven't pushed a wrong button somewhere, and if it can't heat up the water after a minute or two, I'd go shopping.

Oh horrible! Nani why don’t anybody told you about this while buying microwave oven.? You should not cook potatoes in microwave oven otherwise it will go like yours. Additional tip, you should not boil eggs too in the microwave oven. If you try to boil them in your microwave, they will burst and the whole kitchen will stink for days. Don’t try to bake these things in your microwave. Is costly microwave does worth this potato or egg?

How old is it? I've had mine for at least 15 years. That is weird how the potatoes got cooked wrong......are you sure you had them on the right setting? Microwaves are cheap; you can get an inexpensive one anywhere if it needs to be replaced.

Can you take it to a repair shop? Never had that problem.