Dell 2 in 1 has a power issue

My Dell I7 2 in 1 was having issues restarting after I replaced the WiFi cable in the monitor.  

Initially, it worked fine. Then it would only wake up from deep sleep if I disconnected the power cable.  I would plug it back in and it would work fine.

One day, it stopped altogether. The indicator light flashed once and it never came back on again. So, I began the process of elimination.  I removed the battery, no life. Next the wifi card, then the RAM, then the secondary battery. I tried starting it after every component was removed.  I tried a different cable. Nothing.

So I bought a new motherboard and installed it. I charged up the battery and got the indicator light to flash and then nothing.

I'm stumped.