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I've had this happen on three different customer machines over the last few months, and for the life of me I can't figure out a lasting solution.

In all cases, it appeared that the problem occurred after a Windows update. I'm not sure which update in particular. I see a BOOTSECT.bak on the System Reserved Partition with a timestamp that coincides with what the customer told me about the updates. So I'm assuming some update is playing with the boot sector and clobbering everything.

Symptoms:

Computer comes in with BSOD (missing BCD)

I boot to WinRE and check DISKPART:

System reserved partition is fine, but the OS partition is RAW

I perform chkdsk and it says "The first NTFS boot sector is unreadable or corrupt", then proceeds to repair errors in the MFT. After chkdsk is complete, I can see the partition, copy files, etc.

After a reboot, the problem returns, like none of my repairs stuck - I've tried rebuilding the boot sector using bootsect /nt60, and it is successful, but bootrec /fixboot always returns "Access is denied".

I've tried every permutation of search terms I can think of and can't find a solution or even a case of the exact same problem.

All three of these computers are older hardware which originally came with Windows 7 and were upgraded (or clean installed). Two were HP machines, and the current one is a Dell Optiplex 380.

Has anyone encountered this? If I can provide any more information that might be helpful, please let me know!

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    Have you checked the status of the hard disks, by SMART data if supported?
    – harrymc
    Commented Feb 25, 2021 at 18:09
  • @harrymc Yes, and the drives are physically fine - that's what's so weird about this 😞
    – mathiscode
    Commented Feb 25, 2021 at 18:23
  • On some HP machines, I've had issues with BIOS trying to boot using what seems to be an apparently hard-coded .efi filename. If Windows has tried to change the name of the EFI file, perhaps that is part of the issue. My work-around was to rename the preferred boot file to that of the OEM .efi file. This kluge was needed for dual boot, but, as you state, that seems strange for stright Windows PC's. My only other guess is persistent malware.
    – DrMoishe Pippik
    Commented Feb 25, 2021 at 19:02
  • Perhaps a badly-coded boot-sector virus.
    – harrymc
    Commented Feb 25, 2021 at 19:47
  • @DrMoishePippik These machines have all been MBR systems so there's no EFI witchery going on.
    – mathiscode
    Commented Feb 25, 2021 at 19:54

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