Windows 11 Existing Windows 11 not booting

[ZORX]

After buying an extra SSD I decided to dual boot my PC with one SSD being Windows 11 and another being Linux Ubuntu.

Recently I decided to get rid of my Linux drive by cleaning it on DISKPART but after doing so now my Windows 11 drive is not booting or showing up on BIOS, I installed another Windows 11 on my previous Linux drive, booted it up and checked the drives, everything is there and showing up but the drive letters are out of place and scrambled. I can't change the original windows 11 drive letter back to C.
On Disk Management the old Windows 11 drive doesn't have an EFI partition, that might be the problem but I'm not sure.
Could the problem be something else?

Any help with this matter would be highly appreciated.
Many thanks in advance.

 

[ChatGPT]

Hi ZORX — you’re on the right track diagnosing this. Short answer: yes — the missing EFI partition is almost certainly the main problem (UEFI firmware needs an EFI System Partition with Windows boot files to show a disk as bootable), and wiping the Linux disk can also remove a shared ESP or the boot manager that Windows was using. The good news: this is usually fixable by recreating an EFI System Partition and restoring the boot files / BCD.
What probably happened

• You had two drives and the UEFI boot files (ESP) and/or Windows Boot Manager were on the other disk (the one you cleaned). When that disk was wiped the firmware had no boot files for the original Windows install, so the original SSD stopped appearing in the UEFI boot list and wouldn’t boot.
• Installing a fresh Windows on the other disk created a new ESP there, so that drive boots but the old Windows install is left without an ESP and therefore appears offline/unbootable and its partition letters look “scrambled” inside the running Windows.

Safe plan to fix it (overview — I’ll walk you through each step)

1. Backup any personal data you can (from the working Windows or by attaching the drive to another PC).
2. Temporarily disconnect the newly‑installed Windows disk (the one you just installed to) — this avoids confusion and makes sure we repair the original drive as the only boot target. (Optional but recommended.
3. Boot from Windows 11 installation media (USB) → Repair your computer → Troubleshoot → Command Prompt.
4. Inspect disks and volumes with DiskPart (we’ll need your outputs — see request below). If the original Windows disk has no FAT32 ESP, create one and assign it a temporary letter. Then use bcdboot to recreate the UEFI boot files.
5. Reboot, enter UEFI, set the repaired disk as first boot device, test. If it boots, reconnect the other disk and adjust boot order as desired. If it doesn’t, we run a few BCD / bcdedit repairs.

Exact commands (run from the Win11 USB recovery Command Prompt)

• Identify disks and volumes
  diskpart
  list disk
  select disk X (replace X with the disk number of the original Windows SSD)
  list vol
  exit
• If there is NO EFI partition on that disk, create one (example creates a 300 MB ESP and mounts it as Z
  diskpart
  select disk X
  create partition efi size=300
  format fs=fat32 quick
  assign letter=Z
  exit
• Recreate the boot files for the Windows installation on that disk (replace C: if WinRE shows your Windows partition under a different letter)
  bcdboot C:\Windows /s Z: /f UEFI

Notes and troubleshooting details

• Use the drive letter that WinRE assigns to the Windows partition. In WinRE the Windows partition is often not C:, so check with dir C:\ / dir D:\ etc or view DiskPart list vol to find the Windows folder. The bcdboot command must target the real Windows folder as seen in that recovery environment.
• If you get “Access is denied” running bootrec /fixboot, mounting the ESP and using bcdboot as above is the standard workaround.
• If after recreating the ESP the disk still doesn’t appear in UEFI, verify the disk is GPT (UEFI needs GPT) and that Secure Boot / UEFI mode is enabled. Tools to check partition style: Disk Management or diskpart -> list disk (GPT disks show an asterisk under the GPT column in diskpart) or use the System Information (msinfo32) BIOS Mode.
• Drive letters in a running Windows session reflect how the currently‑running Windows assigned them. You generally cannot change the running system volume letter (C while that Windows is running; to change or restore letters for an offline Windows installation you must operate from WinRE/another Windows environment, and be careful — changing letters can break installed programs if done incorrectly. Often the correct approach is to rebuild the boot manager so the original installation is the active boot and Windows will assign it C: when it is the boot OS.
• If multiple Windows installs exist, you can use bcdedit /enum all and then bcdedit /set commands to point the bootmgr/default to the correct partition. Example:
  bcdedit /set {bootmgr} device partition=C:
  bcdedit /set {default} device partition=C:
  bcdedit /set {default} osdevice partition=C:
  (Use the correct identifiers and partition letters as seen in WinRE.

What I need from you to proceed safely

• Paste the exact output (copy/paste) of these two commands run from a Command Prompt (you can run them in either your working Windows or from the WinRE CMD — indicate which):
  1) diskpart -> list disk
  2) diskpart -> list vol
• Also paste the output of bcdedit /enum all if possible (run from the WinRE CMD if the system won’t boot normally).
  With those I’ll give you the exact disk number and partition numbers and the precise commands to run (I’ll point out which letters to use and which disk to operate on so we don’t touch the wrong drive).

Warnings / final notes

• Don’t run destructive commands (delete partition, clean, format other than the small ESP) until we confirm which disk is which. Back up important files first.
• If you prefer, we can also do this with the newly-installed drive still connected — but it’s less confusing to disconnect it while repairing the original drive’s boot files.

If you paste the outputs of list disk and list vol (and optionally bcdedit /enum all) I’ll mark exactly which disk/partition to select and give copy‑paste safe commands to recreate the ESP and restore boot so your original Windows drive becomes bootable again.