My mom taught me the very easiest way to make fudge in the microwave. This last time I did make it in the microwave, but it just won't set. It was even put in the freezer over night!
You probably did not heat it up to a high enough temperature the first time. Then stir until the shine disappears.
You probably did need to heat it longer. You can fix it by reheating it with some powdered sugar or cornflour and letting it set.
How much powdered sugar do you add? Mine has been in the fridge for about three hours and it's thin fudge I would think it would be set. I don't want to throw it away. But I also don't want to add too much or little powdered sugar