Computer won't post with second CPU board installed

[livemeyer]

I bought a barebones Z6 G4 from a reputable seller on eBay.  I purchased all the things it needed to be a complete system - video card, ram, M.2 NVME drive.  Upon startup everything seemed to power up just fine, but the system didn't post.  I started to remove components and troubleshoot what might be bad.  I pulled the battery out to reset any BIOS settings that were not original.  I removed the second board holding the second CPU, and the system booted.  I was able to load Win11 from a USB drive and though I found one 32gb stick or ram to be bad, I nonetheless was able to get my system up and running. 

I began to add back in components (ram, video card, etc) but found that when putting the second chipset board back in, again it wouldn't post. 

I'm wondering if there is a BIOS setting I need to enable for the system to run in the two chipset mode?  Any ideas on how to get this system to post running both chipsets is greatly appreciated.  

[livemeyer]

Thanks for your response.  Currently, I've been in touch with the seller and it is reported that they will be sending me another CPU riser board to install and test.  As far as my research has gone, I have not found any indication that I need to switch on the riser card in the BIOS.  I was hoping I was wrong and that someone here might provide guidance.  

[livemeyer]

Update:  I received the replacement riser card from the seller.  I swapped the second CPU into the replacement riser and attempted a boot.  Again, the computer would not boot/post.  The seller wants me to try swapping the CPU with the mainboard CPU.  I'm not home currently but will attempt in a couple days and then update.