Can't Install Windows 10 to a GPT Partition

[Kelly5G]

I'm pulling my hair out here. Terribly confused ... going around in circles trying different things.

PROBLEM:
Can't install Windows 10 x64 from an OEM disk ... to a Samsung 850 EVO 500Gb SSD ... on a GPT partition. Instead Windows 10 installs on a MBR partition.

SPECS:
Motherboard: Gigabyte GA-Z170X-Gaming 7
Bios version: F7
SSD: Samsung 850 EVO 500Gb ... bare and never used ... this is Drive 0 (aka Drive C)
Media: Windows 10 x64 OEM disk
i7-6700K

BIOS SETTINGS: BIOS Features part of the bios
Fast Boot set to Disabled
VGA Support > EFI Driver set to Enables EFI option ROM (default)
Windows 8/10 Features set to Windows 8/10
CSM Support set to Enables UEFI CSM (default)
Storage Boot Option Control > Legacy Only set to Enables legacy option ROM (default)
Other PCI Device ROM Priority > UEFI Only set to Enables UEFI option ROM only (default)

AHCI is enabled.

WHAT I DID:
1. Insert the Windows 10 disk into the DVD drive.
2. Hit F12 during boot to select the boot priority. F12 detected the SSD and 2 instances of the DVD drive ... one contained the UEFI string and the other didn't. (Note that if "CSM Support" is set to "Disabled" ... NO drives are detected.)
3. Boot using the DVD drive with the UEFI string.
4. Windows started to load but did not give me an option of HOW to format the SSD ... it only gave me the option TO format the SSD and no other information.
5. In the end Windows 10 was installed on a MBR partition rather than a GPT partition.
6. I tried this twice using bare and never used SSD's and had the same result both times.
7. Because I did this twice on bare unused SSD's I used diskpart to change the MBR partition of one to GPT ... so now I have one empty SSD with GPT but I haven't been able to find a way to install Windows 10.

As I understand it ... if I boot to the DVD drive that contains the UEFI string and the Windows 10 disk ... Windows 10 should be installed on a GPT partition. Evidently I'm missing something.

QUESTIONS:
1. What am I missing ... how do I install Windows 10 on a SSD and format it with a GPT partition?
2. What bios settings should I use?
3. Any idea how to get out of this mess?

When you reply assume I'm an idiot ... I'm really not ... but specificity is always helpful.

 Thanks!

 KenB

[ElectroStingz]

Hello,

Change the legacy only option

[pegasis]

I am not understanding what you are trying to say

[shadowsports]

He was referring to the Storage Boot Option Control....  Basically you want UEFI Boot, have to select the UEFI (prefixed) windows installer option (like you did).... which will install as GPT Partition. 

To ensure this happens...  Use shift+F10 during install when selecting your storage device (where you are installing windows to.)  This opens a command prompt and lets you use diskpart to create a GPT partition.

See this KB article for more:

https://docs.microsoft.com/en-us/windows-hardware/manufacture/desktop/windows-setup-installing-using-the-mbr-or-gpt-partition-style