Problems Installing to GPT Disk

ASROCK Z68 Pro 3 updated to P1.40 UEFI/BIOS

Long story:

- Years ago started with a clean install of Win_XP. Made few if any changes to default UEFI/BIOS settings.

- Over the years went to clean installs of Win_7 and then Win_10. No issues. Always MBR style HDDs.


- A few months ago I wanted to move to a GPT style HDD
+ Created back-up image first
+ Tried a Win_10 clean install following Microsoft (MS) instructions for installing to a GPT style HDD
+ Failed!! (have done successfully on several old Dell PCs that support UEFI)
+ Could not boot and could not even restore from back-up image created earlier
+ Had to clean install Win_10 again and slowly and painfully re-create my set-ups of various items. Remained MBR style HDD.


- Yesterday wanted to switch to an SSD and retry a clean install to a GPT style HDD
- Replaced spinning HDD with SSD
- Changed SATA Mode from IDE to AHCI before starting as per ASROCK manual
- Did a Win10 clean install to SSD using MS instructions for installing to a GPT disk
- Installed OK and booted, but disk reverted to MBR style
- Retried a few times, no success
- Tried to switch from SSD back to unchanged HDD
- Failed!!
- Switched SATA Mode back to IDE
- Still failed with message saying HDD repair required
- Finally tried "boot from other operating system" on repair screen
- It offered "Windows 10" and Windows 10 Volume 1"
- Selecting "Windows 10 Volume 1" gets me back to the old Win_10 MBR system, but via the select OS menu

HELP. What am I missing in installing to an GPT style SSD and why do I have to go through that select an OS choice? Only one system disk is in the PC now.

Thanks for any help.

--SD