Whirlpool Microwave not heating

My microwave was working fine. I heated one plate. When I put in the second plate, it made the usual noise, but the turntable was not rotating and the food did not heat at all. Any ideas.

Well, the microwave works when we lift up on the door. Tried to put a washer under the bottom door hinge. Also put some tape on the door latch. Works without holding the door up, but how long will this last? Is there a part for this?::confused: