when I turn the oven on it starts heating fine. then, at some point, it starts beeping, back panel blinking, then stops working, even the clock goes off. I can unplug it and plug back in again and it starts working. sometimes I can use it for a short time but then it goes off again. could it be the thermostat or sensory. model number has kw7.720bd120v after it. the serial # is Ol1877490 with kw10.2120240v6082 after it.