Mac – EFI Boot doesn’t work when trying to boot windows from the Mac

bootefimacpartition

2 years ago, I installed Windows on a external SSD to be booted from my Mac. It used to work well. I would plug my external SDD, hold the option key at the beginning and chose if I wanted to boot on MacOS or on Windows (for windows, the name of the volume was EFI Boot).

But today, something went wrong and the EFI Boot doesn't work anymore. When I choose it, the screen and the mouse freeze and I have to force a power off.

The problem probably comes from the fact that I recently tried to install Linux on another partition of my external SDD. Although, I didn't want it, the EFI Boot file of Linux were placed in the EFI partition of my internal drive. In the end, I deleted Linux and the EFI File generated in the EFI partition of the internal drive. So technically, I didn't touch the EFI partition of my external SSD. But clearly something happened Beauce now it doesn't work anymore.

Do you have any idea what happened?
Is there a way to repair or recreate the EFI partition that would boot on the windows that is already installed on my external SSD?

Thank you!

Best Answer

I found a way to do it.

  • Boot a Windows 7/8/8.1/10 installation media (generated with another functioning windows)

  • On the first screen, press SHIFT+F10 to bring up the command prompt.

  • With the command prompt, use diskpark to erase the Broken EFI partition (you may need to force it with delete partition override)

  • Use diskpart to create a new EFI partition create partition efi size=100

Then, exit diskpart and execute bcdboot X:\windows /s S: /f ALL Note: Replace "X" with the volume letter of the Windows OS partition and S with the new EFI partition

In fact, I had to adjust it to my case but I got some help from here: https://www.tenforums.com/installation-upgrade/52837-moving-recreating-efi-partition.html

Related Question