Turns on and off continuously

As soon as I plug in the power cord and open the laptop, it will start turning on for approximately 4 seconds then off for 7 seconds. The screen remains dark during this process. I removed the back cover and removed the battery and just plugged in power cord and received the same result. Can anyone give me some suggestions on what to do next? My theory is it’s a motherboard issue but it’s just a guess. Any suggestions would be appreciated.