New microwave

Last night I just fancied some popcorn. I make it in the microwave in a Tupperware bowl . I turned the microwave on and I saw sparks of fire, heard sizzling and smelt burning, I turned it off straight away and checked I hadn't put any metal in there. I took the bowl of popcorn out and tried the microwave with nothing in it and the same happened. The microwave is now in the garage awaiting transport to the tip/recycling centre.
I bought this lovely new microwave, haven't tried making popcorn yet!!!!