Use this microwave longer than 3 min. it shuts off & acts like there is no power. After about 20 min. it will come back on as if it was just plugged in for the first time. What's wrong? How do I fix it? If I unplug for 1 min, then plug it back in, doesn't change. still no power. None of the fuses for the house are tripped and all plugs are in good working order. Doesn't matter what plug I use, same thing happens. It has plenty of ventalation, no heat or exhaust is being trapped or restricted.