microwave?

model dmx50 serial mdza12371719 microwave combi grill, never used the grill ever, two years old all, only used it to reheat pre-made food..all of a sudden the microwave just stopped reheating the food, its still turns lights still works but after the minutes are up its still cold thats it. I assume its something like putting in a new heat element however I am not expert and realy don't have a clue even though I know its just one thing. Its a great microwave no other flaws. Please help
iits a delonghi stainless steel interior and exterior model , quite a large one. Thank you