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Converting from BIOS to UEFI

Level 7
Hi all. I have been running this Maximus IX Hero for several years in essentially legacy mode -- at least from a boot perspective. I have an Intel i7 7700K processor with 32GB RAM, TPM 2.0, and an Intel 660p NVMe m.2 system drive running 64-bit Win 10 Pro with the latest updates.

I would now like to convert it to full UEFI mode but am just going around in circles without success and hope someone can help me with the proper setup settings for full UEFI on this mobo. Here's what I have done and the results so far...

I cloned the system drive onto a Seagate HDD and then converted that drive type from MBR to GPT. It converted with no warnings or errors and after adding a new partition it now shows up as a GPT-type drive. I have not been able to get the PC to boot from the GPT drive. Sometimes it just returns to setup, sometimes it gives me a secure boot error saying it has detected changes, and sometimes after exiting setup the cursor goes to the top left corner and will stay like that forever -- I have to manually reboot it.

I'm just about in shotgun mode now so it's hard to learn anything from my changes and subsequent results.

Does anyone know the complete configuration settings to run UEFI mode? Also, any help on what is the proper action to take for the secure boot error?

Thanks in advance for your help.


Level 10
Your startup is failing before Windows Boot Manager gets loaded, which suggests a problem with your EFI System Partition. After converting to GPT, check the drive to make sure the ESP was created properly: You should see a new, small FAT32 partition (usually 100MB) that contains the Boot Manager files.

You didn't mention how you converted the drive, but if you're using Microsoft's official MBR2GPT tool, the ESP should be created as part of the process. Also, if you have multiple drives connected, make sure there's only one ESP present across all drives.

Level 7
Hi and thanks for your reply. I was planning on updating this thread this evening but want to acknowledge your help now.

I had finally stripped things down to the bare minimum, including disconnecting all of the HDDs and using only the NVMe drive on the mobo. Everything worked as advertised. Once up and running on the GPT drive I was able to convert the rest of the drives successfully. Given your post, I think it must have had something to do with the online clone of my system disk -- I use Casper to create/update it weekly.

Everything is good now. Thanks.