Dell XPS 15 (L501X) - Motherbpard replacement issue

Last week, my XPS 15 wouldn't power on. When I plugged the power adapter into the port, the LED light on the cable's tip would go out. A bit of Googling led me to find it was either the charging port or the motherboard.

Since the charging port was the cheaper of the two, I started there. No joy. I then ordered a new motherboard from Dell. After replacing it, the laptop now refuses to power on. The LED indicator on the charging cable remains lit when inserted into the laptop.

What's happening now when I press the power button, is the WiFi indicator light lights up. No activity on the screen, no POST, no anything.
I took it apart again and replaced the CMOS battery, checked for any bad connections, looked for loose wires and can't find anything out of place.

Is there something I might be missing or have overlooked? Is there anything I have to do with the motherboard like flashing it or anything? I just want to determine if I was sent a DOA motherboard before I call Dell on Monday.

 

If all the lights are normal have you tried using it with an external display? You shouldn't have to do anything to the motherboard besides install it...

 

The only light that comes on is the little antenna indicator, not even the power button when pressed. There is no indication whatsoever that the computer is turning on. No POST beeps, no fans...nothing.

Here is a pic of the light after pressing the power button:

 

I have now gone through two replacement motherboards with Dell. I suspected it was the power button or something in between the button and the mobo.

I found a replacement palm rest cover that had all the cables attached. When I installed the replacement palm rest with all the new gear, nothing happened when I pressed the power button. I then tried swapping parts from the new cover to the old one, one at a time. I ended up getting the same results as before.......noting happens except the WiFi indicator lights up.