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[Solved] Windows 10 UEFI Boot Issue: Access Denied on Bootrec /fixboot, and Unsuccessful BCD Rebuild

Andrzej Ch. 33030 12
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  • #1 17486074
    Andrzej Ch.
    Level 33  
    Posts: 2230
    Help: 222
    Rate: 387
    Hello.
    I have had a problem starting my computer since yesterday. Trying to boot the system back to the bios. I have tried various actions with bcdboot and bootrec and it still has problems

    I run the installation of windows 1803 (I have a flash drive with this version of build), go to the console and have the following symptoms:

    Bootrec / fixmbr - correct operation
    Bootrec / fixboot - Access denied
    Bootrec / scanos - finds one windows installation [D]
    Bootrec / rebuildbcd - finds one widnows installation and it doesn't matter if we choose [Y] or [N] or All, I get the following message: Unable to find the requested system device.

    Disk configuration (per diskpart)
    list disk:
    Disk 0 Online 1863GB 0
    Disk 1 Online 476GB 0 GPT *
    Disk 2 Online 14GB 0
    Disk 3 No media

    letter part:
    Disk 0
    partition 1 - primary 1863GB

    Disk 1
    partition 1 - recovery 450GB
    partition 2 - system 100MB
    Partition 3 - Reserved 16MB
    Partition 4 - primary 467GB

    Windows 10 is installed on partition 4 - but I can't run it
    Please help
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  • #2 17486107
    qs300
    Level 33  
    Posts: 2088
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    The easiest way is to disable UEFI in BIOS and then install the system.
  • #3 17486164
    krzychupar
    Level 43  
    Posts: 6807
    Help: 1490
    Rate: 633
    Automatic repair with Startup Repair Tool
    MBR repair
    Command 1: bootrec.exe / fixmbr
    Command 2: bootsect.exe / nt60 all / mbr

    boot sector repair
    Command 1: bootrec.exe / fixboot
    Command 2: bootsect / nt60 C: (repair partition c :)
    Command 3: bootsect / nt60 SYS (repair system partition)
    Command 4: bootsect / nt60 ALL (repair all partitions

    reconstruction of the BCD warehouse
    Command: bootrec.exe / rebuildbcd
  • #4 17486181
    Matuzalem

    Level 43  
    Posts: 17279
    Help: 1651
    Rate: 1079
    I would also, to simplify the situation as much as possible, disconnect "Disk 0" and then take all these repair options (and maybe even start them by checking whether the system will not be able to cope with the system without using commands from the console).
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  • #5 17486273
    Andrzej Ch.
    Level 33  
    Posts: 2230
    Help: 222
    Rate: 387
    unfortunately it does not boot without disk 0
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  • #6 17486315
    krzychupar
    Level 43  
    Posts: 6807
    Help: 1490
    Rate: 633
    To enter all these commands you must have a system CD. You set up boot from disc, boot the computer, click any key, and then you enter the recovery console and enter the commands I gave one by one.
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  • #7 17486334
    Andrzej Ch.
    Level 33  
    Posts: 2230
    Help: 222
    Rate: 387
    system board?
    Not enough pendrive with installer?
    I also tried auto repair and it was not successful
  • #8 17486357
    krzychupar
    Level 43  
    Posts: 6807
    Help: 1490
    Rate: 633
    Pendrive can also be.
  • #9 17486405
    Matuzalem

    Level 43  
    Posts: 17279
    Help: 1651
    Rate: 1079
    Andrzej Ch. wrote:
    unfortunately it does not boot without disk 0


    What is not starting? Lest it immediately turn out that the system and boot were separated and now there is nothing to fix.
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  • #10 17486440
    Andrzej Ch.
    Level 33  
    Posts: 2230
    Help: 222
    Rate: 387
    @Matuzalem
    I have a boot flash drive made with the Win 10 build 1803 installer (made with Microsoft's system image download tool) exactly as installed. Can I use it to try to repair from the admin console mode.
    Do I understand correctly?
    What does it mean "system and boot separated"?
  • #11 17486455
    krzychupar
    Level 43  
    Posts: 6807
    Help: 1490
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    So if the system does not boot without disk 0, it means that this disk has a boot sector and this disk needs to be repaired.
  • #12 17486465
    Andrzej Ch.
    Level 33  
    Posts: 2230
    Help: 222
    Rate: 387
    I followed the instructions given by my colleague @krzychupar

    Below I will list only those that turned out to be wrong:
    bootsect / nt60 all / mbr- for drive F: parameter invalid - unable to open root directory
    \ Device \ HarddiskVolume5 - The parameter is invalid - cannot open root directory

    \ ?? \ PhisycalDrive1
    Bootcode is only updated on MBR. Different partitioning scheme is used on this disk

    bootsect / nt60 SYS - target volumes will be updated with BOOTMGR compatible bootcode
    The system partition not found - The specified system device could not be found

    Bootsect / nt60 ALL
    D: (\\ Volume {xxxxxxxxxxxxxxxxxx} Updated filesystem bootcode. The update may unreliable the volume could not be locked during update. Access denied.
    F: (\\ Volume {xxxxxxxxxxxxxxxxxx} cannot open root directory. Invalid parameter
    \ Device \ HarddiskVolume5 - The parameter is invalid - cannot open root directory

    After that, I started my computer. It is unchanged. The system does not start, after about 10 sec. uefi bios opens.


    One more first symptom that something is wrong were blue screens with the information "Inaccesible boot device" and now it doesn't even have such a message, it just goes to the bios right away

    Please give me further advice. I want to run windows from this drive. The new installation is not taken into account.


    If I turn off the UEFI mode in the motherboard's BIOS, then the system tries to boot, but I get the error: "Inaccesible boot device"
    When I turn on UEFI again for about 1/2 sec. I will flash blue screen of death with error 0xc0000001.
    I don't know what to do next?

    I get alternating blue screens with errors:
    -inaccesible boot device
    - error 0xc0000001


    I can see that no one can help, which is a pity, now I fixed the errors and problems with the inaccesible boot device myself. There was only one problem left for me, that is repairing (replacing, etc.) the file on the boot partition:
    EFI \ Microsoft \ boot \ resources \ custom \ bootres.dll.
    When you try to boot the system, information about the corruption of this file is written to the srttrail.txt file.
  • #13 17742342
    Andrzej Ch.
    Level 33  
    Posts: 2230
    Help: 222
    Rate: 387
    It remains to reinstall the system from scratch.
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Topic summary

✨ The discussion revolves around a Windows 10 UEFI boot issue where the user encounters "Access Denied" errors when attempting to execute the Bootrec /fixboot command and faces difficulties rebuilding the BCD. The user has a Windows 10 build 1803 installation on a flash drive and has tried various repair commands without success. Suggestions include disabling UEFI in BIOS, using the Startup Repair Tool, and disconnecting certain disks to simplify the repair process. However, the user reports that the system does not boot without Disk 0, indicating it contains the boot sector that needs repair. Ultimately, the user considers reinstalling the operating system from scratch after unsuccessful repair attempts.
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FAQ

TL;DR: On UEFI PCs, Windows boots from an EFI System Partition; Microsoft lists "EFI system partition: 100 MB". Fix "bootrec /fixboot access denied" by mounting the ESP and rebuilding boot files with bcdboot. [“UEFI/GPT-based hard drive partitions”]

Why it matters: This FAQ helps Windows 10 users fix UEFI boot failures without reinstalling, even when bootrec and automatic repair fail.

Quick Facts

  • UEFI Windows boots from a FAT32 EFI System Partition (ESP), minimum 100 MB, on a GPT disk. [“UEFI/GPT-based hard drive partitions”]
  • Rebuild UEFI boot files from WinRE: bcdboot C:\Windows /s S: /f UEFI. [“BCDBoot Command-Line Options”]
  • Bootsect updates MBR/volume boot code (BOOTMGR/NTLDR) for BIOS-style boots, not UEFI. [“Bootsect Command-Line Options”]
  • GPT layouts also include a Microsoft Reserved (MSR) partition of 16 MB for Windows. [“UEFI/GPT-based hard drive partitions”]

How do I fix “bootrec /fixboot — Access is denied” on a UEFI Windows 10 PC?

UEFI uses the EFI System Partition (ESP), not NTFS boot sectors. FixBoot targets BIOS-style boot code, so it often fails. Mount the ESP in WinRE, then rebuild boot files with BCDBoot. Example: bcdboot C:\Windows /s S: /f UEFI. As Microsoft puts it, “BCDBoot copies boot files to the system partition.” Reboot and select Windows Boot Manager in firmware if needed. [“BCDBoot Command-Line Options”]

What’s the step-by-step way to rebuild UEFI boot files with bcdboot?

  1. In WinRE Command Prompt: diskpart → select the 100 MB FAT32 EFI partition → assign letter S:.
  2. Exit diskpart, then run: bcdboot C:\Windows /s S: /f UEFI.
  3. Restart and ensure the firmware boots the Windows Boot Manager entry on that disk. [“BCDBoot Command-Line Options”]

Why does “bootrec /rebuildbcd” return “Unable to find the requested system device”?

On GPT/UEFI, there is no “active” partition and the BCD lives on the ESP. If the ESP isn’t mounted or targeted, rebuildbcd cannot locate it. Mount the ESP, then use BCDBoot to create the boot files and BCD store on that partition. Command: bcdboot C:\Windows /s S: /f UEFI. [“BCDBoot Command-Line Options”]

My system only boots with Disk 0 connected, but Windows is installed on Disk 1. What happened?

Your boot files likely reside on an EFI System Partition on Disk 0, while Windows lives on Disk 1. Removing Disk 0 leaves the firmware without boot files, so the PC drops to BIOS. Edge case confirmed in the thread: the PC would not boot without Disk 0 attached. Recreate boot files on the OS disk’s ESP to decouple. [Elektroda, Andrzej Ch., post #17486273]

Should I disable UEFI and reinstall in Legacy BIOS to solve boot issues?

No. Windows 10’s supported layout is UEFI on GPT with an ESP and MSR. Switching to Legacy changes the boot path and can break existing installs. Repair the UEFI boot files and BCD on the ESP instead of downgrading firmware mode. [“UEFI/GPT-based hard drive partitions”]

What causes INACCESSIBLE_BOOT_DEVICE or 0xc0000001 after changing BIOS/UEFI settings?

Changing from UEFI to Legacy, or altering storage modes, can orphan your boot path. Windows then cannot access the system partition. Microsoft states the bug check “has lost access to the system partition or boot volume.” Restore original firmware settings and rebuild the UEFI boot entry if needed. [“Bug Check 0x7B: INACCESSIBLE_BOOT_DEVICE”]

How can I repair a bootres.dll corruption mentioned in SrtTrail.txt?

Run System File Checker offline from WinRE to replace corrupted files. Identify your Windows drive, then run: sfc /scannow /offbootdir=X:\ /offwindir=Y:\Windows. Replace X: and Y: with the correct letters. If SFC fixes files, reboot and test. If not, proceed with UEFI boot repair using BCDBoot as a next step. [“Use the System File Checker tool to repair missing or corrupted system files”]

Bootsect says “The parameter is invalid” on my GPT disk. Why?

Bootsect updates MBR or volume boot sectors used by BIOS-era loaders (NTLDR/BOOTMGR). UEFI boots from the ESP instead, so pointing bootsect at GPT/UEFI layouts yields errors or no effect. Use BCDBoot to place the correct boot files on the ESP for UEFI systems. [“Bootsect Command-Line Options”]

How do I identify the right EFI System Partition in DiskPart?

In WinRE, open diskpart and run list vol. Look for a small FAT32 volume around 100 MB marked System or EFI. That is the ESP. Select it and assign a temporary letter, for example S:, so BCDBoot can target it during repair. [“UEFI/GPT-based hard drive partitions”]

Bootrec /scanos found Windows on D:. How do I point repairs to the right Windows folder?

Drive letters in WinRE differ from normal Windows. Confirm the Windows folder by checking each volume, then feed that path to BCDBoot. Example: bcdboot D:\Windows /s S: /f UEFI. This writes the correct boot files for that installation. [“BCDBoot Command-Line Options”]

Can I run these repairs from a USB installer instead of a DVD?

Yes. Boot the Windows installation USB, choose Repair your computer, and open Command Prompt. From there you can run diskpart, bcdboot, and sfc. This avoids a full reinstall while giving full recovery tooling. [“Recovery options in Windows”]

Startup Repair failed repeatedly. What should I try next?

Use Advanced options in WinRE. Manually mount the ESP and run BCDBoot to rebuild boot files. Then check system files with SFC. If boot still fails, back up, then use Reset this PC or a repair install as a last resort. [“Recovery options in Windows”]

What partition sizes are typical on a healthy Windows 10 UEFI disk?

Typical layout includes an EFI System Partition of 100 MB (FAT32) and a Microsoft Reserved (MSR) partition of 16 MB. The Windows partition consumes the remaining space as NTFS. These sizes help firmware and Windows manage boot and disk metadata. [“UEFI/GPT-based hard drive partitions”]

After moving drives, firmware jumps straight to BIOS without errors. What should I check?

Ensure the disk with the ESP is present and first in the UEFI boot order. If the ESP moved or is missing, recreate boot files on the current OS disk with BCDBoot. Then select Windows Boot Manager for that disk in firmware. [“BCDBoot Command-Line Options”]

When is a clean reinstall the pragmatic option?

If BCDBoot repairs, SFC, and Startup Repair all fail, and hardware is healthy, reinstalling saves time. Back up data, then use Reset this PC or clean install from USB media. This restores a correct UEFI/GPT layout and boot path. [“Recovery options in Windows”]
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