The most common problem with my microwaves have been a blown fuse. Unplug the microwave from the wall, take the screws found on the back or sides of the cabinet and pull off the cabinet and look for a fuse. Pull the fuse out and test it with a ohm meter or continunity meter. If you don't have a meter go to Ace Hardware or other home improvement center and get a new one and see if that fixes it.