Windows 10: Dual boot win7/win10 MBR/UEFI problem, cannot reinstall Win 10 ISO

I've been an insider since FEB. Last ISO I installed was 10074. Since updating to 10240/rtm things have gotten buggy, apps don't function, can't update etc.

I want to install the latest ISO on the 10240 oartition, but when I try I get, "Windows cannot be installed to this disk. The selected disk has an MBR partition table. On EFI systems, Windows can only be installed to GPT disks."

The solution is to adjust those boot parameters in the BIOS, make everything legacy/MBR, so I've read. Problem is, the bios is locked down, it's a HP Envy laptop. The BIOS supports both MBR and GPT, however, GPT is the default, and legacy boot options only kick in when GPT is not supported. There is no way to change this. So, I have MBR for recovery and Win 7 partitions, and selecting any partition installing Win 10 gives me this error.

Is there a work around?

(I can not reset because of the inaccessible boot device bug, maybe related, besides I need the ability to reformat that partition being an insider)

It's really frustrating as up until build 1074, this was not an issue.

:)

 

After Windows 10 PC reset, inaccessible boot device

Easy fix for ....On efi systems windows can only be installed to GPT disks - [Solved] - Windows 7

Thinking,

Because I was in a dual boot using MBR, after about 4 windows10 loopboots using UEFI to my Win10 partitionI, my Bios defaulted to legacy boot using MBR on a win 7 machine. That's why it was not infinite.

I prepared a USB using the media creation tool on my win 10 partition, and tried to reinstall win10, only to receive the error, "Windows cannot be installed on this disk. The selected disk has an MBR partition table. On EFI systems, Windows can only be installed
on GPT disks."

In my bios, which is pretty locked down (HP Envy), I can only select legacy boot enabled/disabled, but UEFI is the default, and MBR is secondary. I am going to prepare a second USB in my Win 7 partition, which should force the media to be MBR, and not
GPT, like my original ISO from way back, and see what happens.

 

Temporary Hide OS Partition

Some things to consider; type of bios- uefi or legacy or both, hard drive partition scheme-mbr or gpt.

Clone the win7 drive so if there is an issue with win10 and the win7 drive connected at the same time

you have some insurance; test the cloned drive.

The win10 install on fresh ssd; is this a full retail, oem, or upgrade from win7 ?

What win7 is installed, oem or retail ?

Hiding, deleting the win7 partition ( current boot ) may make the entire drive unusable because it

contains the drives boot layout information.

If the pc has uefi it supports drives above the 2tb os bootable from win8.1.

Remove win7 drive from pc, install ssd, install win10, get the os to current build.

Reconnect win7 drive, go into bios, make sure win 10 boot loader is first option,

then the physical drive windows is installed on, than other boot options;

if this is not done, win7 could still boot and the next win10 boot will find

corrupted data on the win7 drive.

Easybcd is a good program for modifying the boot loader.

 

I'm thinking reinstall build 10074, and then try to update, but this does not really help going forward. Is there a a non destructive way to make my Win 7 partition GPT?

 

- Delete all partitions on the disk, so you can use GPT (GUID Partition Table).
- But if you want to use MBR (Master Boot Record) partition table, then boot from the Windows installation media in Legacy BIOS Boot Mode.

Quote from this post: UEFI Boot Mode (installing using the GPT partition style) and Legacy BIOS Boot Mode (installing using the MBR partition style). -> link

 

to force boot in MBR mode rename "bootmgr.efi" to "bootmgr.efi.old"

you can also rename the "EFI" folder to "EFI.old"

this will sort of disable the setup media's UEFI booting

 

Where would I do this?

 

I was wanting to save the Win 7 partition, but even if I nixed it and everything went to hell, would I be able to reformat using HP recovery media? Or would I end up not being able to boot their discs because the HD was converted? It's an OEM license and software.

 

Found it, but I'm in my win 10 partition with admin privileges, but renaming is not an option. Would it be in Win 7?

 

I was able to rename the "bootmgr.efi" to" bootmgr.efi.old" in the ISO after rebooting to win 7 (this alone is a cause of concern). But it did not work, at least for me.

 

I created a new USB using an older USB 2 only drive. It then appeared in the boot manager with both MBR and UEFI options for booting, and I was able to install using the MBR option. The other drive did not give me the MBR/legacy option.