Whirlpool over the Stove Microwave

I just purchased a Whirlpool over the stove microwave from Lowes (this past Saturday). I installed the unit the same day and after installation ran the unit for 2 minutes to heat a cup a water to confirm the unit worked properly. The next day, I used to microwave for approximately 30 seconds to heat some left overs. The following day (monday), it was noticed the units wasn't operating. The clock display was off. I proceeded to check the circut breaker to see if it tripped. It didn't and shut off and turned back on. The unit still showed no signs off power on the clock display panel. I also confirmed the circuit breaker was a 20 amp with the only appliance running on that breaker. I unplugged the microwave and after 5 minutes plugged it back in the clock display went back on. After 1 minute, without running the unit the clock went off again. I repeated this step and the same thing happened again, then ext time I ran the unit for 45 seconds and the microwave shut down after 45 seconds in the middle of a time cycle. Next I ran an extension cord to another outlet outside the kitchen, with the same scenario happening. The microwave shuts off after 30 sec to 1 minutes without even running the microwave. Any way have an idea of what the issue is. By the way, checked the circuit out and it wired correctly. The same circuit was used for a prior microwave that was operable for over 12 years. Thanks.