Examkin

Question

Difficulty: HardTroubleshooting Windows OS Startup and Boot Errors

A desktop computer running Windows 11 fails to start after a technician cloned the OS drive from a legacy MBR disk to a new NVMe SSD utilizing GPT partitioning for UEFI booting. On startup, the screen displays 'An operating system wasn't found.' The technician boots into the Windows Recovery Environment (WinRE) command prompt and attempts to run `bootrec /fixboot`, but receives an 'Access is denied' error message. Which of the following command sequences should the technician perform to repair the boot files?

  1. Use `diskpart` to assign a drive letter to the EFI System Partition, then run the `bcdboot` command pointing to the Windows installation directory and target partition.Answer
  2. B
    Execute `bootrec /fixmbr` followed by `bootrec /rebuildbcd` directly from the WinRE command prompt.
  3. C
    Run `chkdsk C: /r` to locate bad sectors on the OS drive, followed by `sfc /scannow /offbootdir=C:\ /offwindir=C:\Windows`.
  4. D
    Open Computer Management MMC from WinRE to set the main OS partition as active.

Answer

Use `diskpart` to assign a drive letter to the EFI System Partition, then execute the `bcdboot` utility referencing the Windows installation path and target volume.
On modern UEFI systems utilizing GPT disks, the standard legacy boot repair tool `bootrec /fixboot` frequently fails with an 'Access is denied' error because the boot files reside within a separate FAT32 EFI System Partition (ESP). The appropriate resolution involves using `diskpart` within WinRE to assign a letter to the hidden ESP and running `bcdboot C:\Windows /s <letter>: /f UEFI` to re-create the Boot Configuration Data (BCD) environment.

Step-by-Step Solution

1
Identify the environment and root cause of the error
The target disk uses GPT/UEFI architecture following a clone, meaning legacy MBR repair tools like `bootrec /fixboot` will fail or return 'Access is denied'.
UEFI boot relies on files stored inside a dedicated FAT32 EFI System Partition (ESP) rather than an MBR boot sector.
2
Mount the EFI System Partition using `diskpart` in WinRE
Select the system disk, select the hidden FAT32 partition (ESP), and execute `assign letter=S:` (or another available volume letter).
Assigning a drive letter makes the hidden ESP accessible to command-line repair utilities.
3
Recreate the EFI boot environment using `bcdboot`
Execute `bcdboot C:\Windows /s S: /f UEFI` to copy fresh boot files to the ESP and generate new BCD boot entries.
The `bcdboot` utility compiles all essential UEFI boot configuration data required to initialize Windows from a GPT drive.

Key Concept

Troubleshooting UEFI/GPT Windows Boot File Corruption via BCDBoot and Diskpart
Estimated Time:2m 30s
Rate this question

Topics

Troubleshooting Windows OS Startup and Boot Errors

More questions from this topic