Windows not booting after converting from mbr to gpt

You delete all the partitions yourself if there are any on the drive.

But, If the entire drive is already GPT and let`s say you have a Data partition, you do not have to touch that partition, you just have to delete the rest of the drive to unallocated space.

Then you can install windows to that unallocated space and it will make the proper partitions, I have done it in the past with no problems.

Do you have the motherboard setup properly ?

CSM has to say UEFI only, not other OS

I would have left it alone, my Z170 is MBR and I have no intention of changing it, there`s no need.

Well, if the drive is GPT now and you want windows, then either clean install windows after deleting all the partitions you don`t need, including any Recovery partitions.

Or maybe Navy will help you with the small 16MB EFI partition if you want to wait.

Then there is another option you are missing, did you enable Secure boot ?

Ya I don`t think it is either.

Let me look at my Z170 Bios and I`ll be back.

The only other option I had to change, and I think you already tried it was Boot\Secure Boot, under that it has to say Windows UEFI Mode.

I don`t know why you think you could install Windows on a GPT drive if you say you saw no UEFI option in the Bios in your 2nd sentence

You have to make sure all the options are there before you convert.

CSM should be Enabled and you can have it set to UEFI and Legacy OPROM, you don`t have to choose one or the other.