Asrock 990 FX killer with Samsung SM951

First, what board do you have, it seems to the the Fatal1ty 990 FX Killer, is that right? - YES

Regarding BIOS changes, in order to make these SSDs bootable you must enable a sub option of the CSM option, found in the ACPI Configuration screen.

With CSM Enabled, set the Launch Storage Oprom to UEFI Only. - DONE

That is only the beginning, other things in the BIOS must be set correctly. They are:

In Advanced/Storage Configuration screen, SATA Mode must be AHCI or RAID. - AHCI

In Advanced/Storage Configuration screen, set AMD AHCI BIOS ROM to Enabled. I'm not 100% sure this needs to be Enabled, you can try it both Enabled and Disabled. - Tryed both.....

In Advanced/Storage Configuration screen, SATA IDE Combined Mode must be Disabled. That is the default in newer BIOS versions. DONE

Question: You have said many times that you cannot find the SM951 shown in the BIOS, right? - YES

Since your board has a M.2 port, there should be an entry for the M.2 port in the Storage Configuration screen, even if nothing is in the M.2 port. That is how it works with my (different) ASRock board. I must scroll down in the Storage Configuration screen to see the M.2 port entry. - There are no M.2. Only SATA3_1-2-3-4-5 and ESATA1

The SATA III ports are listed even if no drives are connected to them. The same should be true for the M.2 port. - I should expect so also......

Are you sure there is no entry for the M.2 port on the Storage Configuration screen? - YES

Next, installing Windows. You may now know you cannot install Windows to a SM951 from a Windows 10 disk, it MUST be done from an ISO on a USB flash drive. If you don't know how to create the USB flash drive ISO installer, let me know. - I have DVD ISO with build 10240.

When you use a USB flash drive with a Windows 10 ISO, do you select it in the Boot Order screen in the BIOS? - press F11 in POST. I Install with no other SSD Attached than SM951.

Do you see TWO entries for the USB flash drive, one that is "UEFI: Flash Drive", and the other, "AHCI: Flash Drive" in the Boot Order list? - Do not remember - I will tell you next time.

You should see these two entries in the Boot Order list, and you MUST choose UEFI: Flash Drive. - I will.

Now we will assume you have booted from a Windows 10 ISO on a USB Flash Drive. The Windows installer is running, and you are on the Standard or Custom install option screen. You MUST choose the Custom Install option. - Always done that.

In the Custom installation screen, you should see the SM951 listed. If not something is wrong, quit the installation. - It is listed, but windows will not install due to expecting that it is not bootable.

If the SM951 is listed, great! Next, delete ALL the partitions on it! All the space should be Unallocated. - Allways do that.

Then click on New to format the SM951. You'll see a message about extra partitions being created, just click Ok. When that is done, you should see four partitions listed from the format. Select the Primary partition for Windows 10, and continue with the installation. It should go quickly.

It is more difficult to manually format the SM951 with all the REQUIRED partitions that the Windows installer will create automatically. Let Windows do the formatting in this situation. - Always formatt disks.

Let us know if any of this helps you get Windows 10 installed and running on a NVMe SM951. If it does, it will be the first time I've known that to work on an AMD board. Otherwise I'll see what else I can do to help you.

One more thing I noticed about your board. The M.2 port is a PCIe 2.0 x2 10 Gb/s interface. Both of the SM951 SSDs are PCIe 3.0 x4 32Gb/s interface drives. You won't get the full performance from your SM951 unless your board has a PCIe 3.0 x4 32Gb/s M.2 port, sorry to say. - I expected so due to the 10GB/s - but IOPS test show up to SM951 specs. Thar will help :)