Dual boot MB; 1 MBR, 1 GPT drives, GPT won't boot, same O/S

[videobruce]

Specs;
Gigabyte GA-970A-D3P Rev 2 older MB (2016) AMD based system.
Main drive; 250GB SSD W7 Pro x64 MBR no hidden partitions
Backup; brand new 4TB same O/S GPT one created System partition using Disk Part .

Backup is seen in the Bios, but won't boot even if the SSD is disconnected. The MB is advertised as "dual boot". No custom settings, no overclocking etc. I've tried different Boot settings, the few that are there and no difference. The system always boot to the MBR. I haven't reset the Bios since I don't do custom settings, but I considered it.

The original system was the SSD and 2TB MBR Backup drive (no hidden partitions), same O/S's and that worked for eight years. Both drives have other storage partitions.

Any other details, please ask. The basic difference is one MBR and one GPT drive.

 

[videobruce]

Here is the Bios boot mode select screen.

 

[pendragon1]

dualbios is different from dual boot, never even heard of that(beside boot managers). what your looking at is just how it allows the uefi to access legacy stuff. if you switch to uefi only, the gpt one should boot. what you should do it convert the mbr to gpt and set it to uefi only, then it should work.

 

[videobruce]

I tried that, but it still won't boot as of now.

 

[pendragon1]

I tried that, but it still won't boot as of now.

check if the bios has a raid mode enabled, make sure its on ahci, and that all legacy stuff is turned off.
are you just trying to transplant these from an old machine to new?