Hello thanks for your inquiry
Try unplugin the unit and plug it back in is this the same popcorn you have always use/
If it does it again you will need to order a sensor for it. Be carefull when opening the microwave their could still be 2000 v even thought it is unpluged the capacitor need to be discharged. To order your part or for a local servicer call 1-800-661-3291they will assit you.
Good luck if this is the right answer please accept