HDD not listed in UEFI mode even after GPT conversion.

dcd98 · 09 Jun 2017

Hello everybody,

i need help with something.I was using the legacy bios mode (MBR) for a long time now but i wanted to switch to UEFI mode so i used mbr2gbt.exe to convert my hdd to GPT after the conversion was complete it said on the black screen that i had to change my boot mode to UEFI in order to boot into windows 10 so i restarded my computer and entered the bios and i changed my boot mode from LEGACY+UEFI to UEFI then i saved everything and rebooted my pc but for some reason it doesn't boot to windows it boots to EFI Shell and both my Hard Disk and my DVD-RW are missing from the boot priority list.Please i need assistance with this situation

Thank You :)

By the way I'm from Turkey so sorry for bad english :)

dalchina · 09 Jun 2017

Hi, the Windows partition layout for an EFI booting system is quite different to that for one using legacy BIOS.

The first has 4 partitions, the second, 3.
BIOS/MBR-based hard drive partitions | Microsoft Docs
UEFI/GPT-based hard drive partitions | Microsoft Docs

A legacy BIOS cannot boot an OS on a GPT disk.

Thus your disk is unbootable as you've found.

Now I could tell you how to take a valid Windows partition from one GPT disk to another and create a bootable system.
What I don't know whether that would work with a Windows partition created under legacy BIOS.

I'll be interested to see what others suggest as I don't want to play guessing games.

How big is your disk?
Do you have a backup or disk image of your original BIOS disk?

dcd98 · 09 Jun 2017

1.Size of the hdd is 1TB
2.I don't have backup of bios

spunk · 09 Jun 2017

Try changing it back to Legacy+UEFI. If that fails,
I would start fresh reinitialize the drive GPT and Install Windows with the GPT+UEFI option. Loosing all data.

Change the Bios to Legacy,
Boot off of Windows install Media, choose your Language and press Shift+F10 to go directly to the Command Prompt.
Here type Diskpart and press enter. At this prompt type the following Bold commands and press enter after each one
ii) list disk
(ie) DISKPART > list disk
It now lists disk by number
you have to select the disk next with
iii) select disk <disk number>
(ie) DISKPART> Select Disk (disk number) = as listed in previous command. The selected disk now has an Asterisk next to it.
iv) clean (this erases all data on the Disk, so be sure you choose the correct one)
(ie) DISKPART> clean
v) convert gpt
vi) create partition primary
vii) format fs=ntfs quick
now for verification of disk status and free space type
v) list disk
the status should be "online" and free space should be "disk size"
‘vi)exit
Remove install media, Shut down computer
On another computer, if you have a Windows ISO image, create a bootable GPT/UEFI USB Windows installer with Rufus. Be sure to change Partition Scheme to GPT for UEFI.
Put the USB Flash drive in the troubled computer, boot into Setup (Bios) change Boot mode to UEFI Restart the computer and go back to the Bios Boot Tab, the Flash Drive should now be listed as bootable media, move this to First Boot Device, Save and Exit.

dcd98 · 09 Jun 2017

spunk said:

Try changing it back to Legacy+UEFI. If that fails,
I would start fresh reinitialize the drive GPT and Install Windows with the GPT+UEFI option. Loosing all data.

Change the Bios to Legacy,
Boot off of Windows install Media, choose your Language and press Shift+F10 to go directly to the Command Prompt.
Here type Diskpart and press enter. At this prompt type the following Bold commands and press enter after each one
ii) list disk
(ie) DISKPART > list disk
It now lists disk by number
you have to select the disk next with
iii) select disk <disk number>
(ie) DISKPART> Select Disk (disk number) = as listed in previous command. The selected disk now has an Asterisk next to it.
iv) clean (this erases all data on the Disk, so be sure you choose the correct one)
(ie) DISKPART> clean
v) convert gpt
vi) create partition primary
vii) format fs=ntfs quick
now for verification of disk status and free space type
v) list disk
the status should be "online" and free space should be "disk size"
‘vi)exit
Remove install media, Shut down computer
On another computer, if you have a Windows ISO image, create a bootable GPT/UEFI USB Windows installer with Rufus. Be sure to change Partition Scheme to GPT for UEFI.
Put the USB Flash drive in the troubled computer, boot into Setup (Bios) change Boot mode to UEFI Restart the computer and go back to the Bios Boot Tab, the Flash Drive should now be listed as bootable media, move this to First Boot Device, Save and Exit.

Thank you so much <3 it worked Thank you all for all the assistance