Dell Latitude E7450 in the Ditch

I purchased a Dell E7450 on Ebay this past year. It worked for months and then one day would only give me a blank screen and diagnostic indicator light. The E7450 provides the following codes:

Storage LED Solid
Power LED Blinking
Wireless LED Solid
Fault Description The memory modules are detected but encountered an error.

I purchased another memory stick to test both stick bays on the motherboard. I purged electricity in the laptop with each attempt at testing the stick combinations, but always received the above
results. I also tried replacing the CMOS battery after purging power in the laptop. I tried disconnecting the screen from the motherboard and then using an HDMI cable to a monitor I know works,
I started the machine, but received the same blinking Power LED.

Before spending more time and money on attempting to understand the problem, I took the laptop to a company that ran their own diagnostics tests. They told me that the issue was with the
central processor. With that I purchased a matching refurbished motherboard, installed it including the paste for the heatsink. I was certain that the new motherboard would solve the problem,
but when I started it up, I received the same blinking Power LED.

This problem is beyond what I know how to do and it seems it is beyond what a company with diagnostic tools can figure. I'm open to any suggestions this forum can provide. I very much appreciate your help.

Doughboy1979