T7910 won’t post - possible memory issues?

I’m having issues getting my Precision T7910 with dual E5-2697 V3 and 128gb memory to post, show any display output or power to usb keyboard.  Power supply tests green and when I turn on the system I get a solid white power button, just no bios or any screen display even if I hit f2 or f12 immediately after powering on.

some history - ever since I purchased this system as refurbished back in 2019, it would occasionally exhibit this issue on initial power up but if I cycled the power it would always boot fine on the 2nd try. Fast forward to a few weeks ago and see suddenly one day it would just not post at all. At that point I gave it a good interior dust cleaning and checked all the connections and then fired it back up and this time it posted!  I ran the full suite of diagnostic and everything passed including all 128gb of memory. I noticed the following repeated in the most recent bios event logs…

-Invalid configuration information - please run SETUP program

-Time-of-day not set - please run SETUP program

“Ah Ha!  It’s probably just a dead cmos battery” I thought, so I took out the old coin cell, waited about 15 min and popped in a fresh one.  Ever since then I’ve not been able to get it to post again. At this point I’m suspecting a memory issue and upon closer inspection I realized that there are two different brands modules, 8x8gb of Samsung (white banks) and 8x8gb of Hynix (black banks).  I removed all of the Hynix sticks, leaving banks 1-4 for both CPUs populated with the Samsungs. When I tried to boot in this configuration I got the Amber 2,7 power LED which supposedly means a memory configuration error.  Next I removed the memory from banks 3 & 4 for both CPUs and it went back to the solid white power LED with no video signal or power to the keyboard. 

Next I’m planning to try 1 stick of the Hynix in  bank 1 only for both CPUs just to rule out bad Samsung memory, but beyond that I’m not sure what else to try.  I’ve also tried another video card that’s known to be working in my T7610. I supposed I could get two approved 4gb crucial modules to test but not sure it’s with the money and effort for such and old workstation.  It’s still a great render box when I need one so I’d love to get another year or two of life out of it.