The microwave oven was working great until today. I closed the microwave to and pressed the appropriate time and start button but the display reads "DOOR" and then doesn't do anything. Additionally, I have noticed that the light doesn't come on anymore when you open the door. I thought that maybe the door wasn't closed properly but it seems to be catching on the appropriate notches when it is closed. The clock and oven included in the unit below seem to working fine. Not sure what's going on? Please help.