GE model je2160 microwave does not heat up food anymore?

6 months ago, my wife cooked a bunch of raw potatoes. Afterwards, the microwave would power on but would not cook. It began working again after a while with no troubles since until she put another batch of potatoes in it again. This time its not fixing itself. Power comes on and seems like normal operation but food is still cold. No codes have come up. Any help is greatly appreciated.