Inaccessible Boot Device - help with diagnosis

Question

I have Windows 10.

On booting my PC, it failed to boot with "Inaccessible Boot Device". It looks as though a Windows update was the catalyst to this failure. Nothing on the PC changed, the disk is fine.

So how do I find out what has gone wrong?

By using a recovery disk, I've renamed various files to try to work out where it has failed.

1. The BIOS correctly finds bootmgfw.efi and runs it.
2. boomgfw.efi correctly finds winload.efi on the C: drive and runs it.

(I know this because if I rename winload.efi on the C: drive, the error changes to a missing winload.efi message...)

3. It looks as though winload.efi is correctly looking for ntoskrnl.exe and hal.dll

(I know this because if I rename either of these files, the error changes to match the missing file I've renamed...)

4. It looks as though winload.efi is correctly finding the System registry hive in c:\windows\system32\config.

(Again, because if I rename c:\windows\system32\config\system the error message changes)

5. It looks as though the boot process isn't getting as far as loading smss.exe.

(Because if I rename that file, the error message remains INACCESSIBLE BOOT DEVICE)

6. Adding either the bootlog or sos options into the BCD for winload.efi does nothing - so I assume the boot process hasn't got this far.
7. I've checked the MountedDevices registry key and it looks good. The \DosDevices\C: key contains the usual DMIO:ID: followed by the 16 byte GUID which appears to match the GUID for the volume (mountvol c: /L).

So can anybody help me to diagnose this issue? How does windows decide to issue INACCESSIBLE BOOT DEVICE. It looks as though the computer pauses for around 20-25 seconds (some sort of probe timeout?) before the message finally appears. There is no disk activity during this period.

Various sources say that INACCESSIBLE BOOT DEVICE means that windows isn't able to locate the boot device - which is fairly incredible given that it's got so far into the boot process and has actually accessed it several times! So I'm guessing this is some of error at a transition point - say from running winload.efi to running the kernel ntoskrnl.exe.

But how can I track down the error?

One interesting question is how does windows, given the entry in MountedDevices, know how to access the device (ie which driver to use). The data consists of the DMIO:ID: signature followed by a 16 byte GUID - does the DMIO:ID: bit somehow tell Windows which driver to use to access the device, and if so which driver?

Answer 1

Power on and off your computer three times

On the third time, your computer will boot into the Advanced Recovery environment

Click Advanced Options

Click Troubleshoot

Click Advanced Options

Click Command Prompt (Admin)

Confirm the drive letter for the Windows image. Usually D: –> dir d:

Run the following to view the installed packages which will also show a date of install.



Dism /Image:D:\ /Get-Packages



Find the package(s) that were just installed by date. Run the following command on the last installed package:



example: dism.exe /image:d:\ /remove-package /packagename:Package\_for\_KB4014329~31bf3856ad364e35~amd64~~10.0.1.0



Reboot.

If you can't get to the recovery menu, go to a working computer.

How to download official Windows 10 ISO files

	[http://answers.microsoft.com/en-us/windows/wiki...](http://answers.microsoft.com/en-us/windows/wiki/windows_10-windows_install/how-to-download-official-windows-10-iso-files/35cde7ec-5b6f-481c-a02d-dadf465df326)

Boot from it and choose the option to repair your computer and choose the Command prompt in the recovery environment.

Answer 2

Inaccessible Boot Device error sometimes can be solved by resetting the BIOS or UEFI firmware to defaults: http://www.mydigitallife.info/comprehensive-lis...
Report back present settings for UEFI, CSM or Legacy BIOS, Secure Boot, and Boot Priority order - first place should be Windows Boot Manager for a UEFI BIOS or Windows hard drive for Legacy BIOS.

If not follow the standard steps to recover when WIndows cannot start below, and aif necessary Advanced steps in this tutorial which includes everything: http://answers.microsoft.com/en-us/windows/wiki...

1. Use whichever method works in this link to access Advanced Startup Options: https://www.tenforums.com/tutorials/2294-advanc.... Easiest may be to restart PC three times to trigger the Startup Options.
2. If none of the other methods work it may be necessary to Create Windows 10 Installation Media on another PC: http://windows.microsoft.com/en-us/windows-10/m...

Insert media, boot it by powering up PC while pressing the BIOS Boot Menu Key: https://www.sysnative.com/forums/hardware-tutor...

Choose the boot device as a UEFI device if offered, then on second screen choose Repair Your Computer. If the media won't boot you may need to enter BIOS/UEFI Setup (pressing key given in chart in link above) to turn off Fast Boot or Fast Startup first.

3. In the Advanced Troubleshooting options try to System Restore to a point before the problems began, Startup Repair, then if necessary from Startup Settings try to get into Safe Mode with Networking, or lastly Safe Mode.

If Startup Settings aren't available you can force Safe Mode from Command Prompt using the command to unhide F8 Advanced Startup Options here: https://www.digitalcitizen.life/4-ways-boot-saf.... Try Last Known Good Configuration and then Safe Mode with Networking.

4. From Safe Mode w/Networking work through the Windows 10 Install Integrity Checklist to make sure the install is set up correctly, optimized for best performance, and any needed repairs get donehttp://answers.microsoft.com/en-us/windows/wiki/windows_10-performance/windows-10-performance-and-install-integrity/75529fd4-fac7-4653-893a-dd8cd4b4db00: If it doesn’t fix Windows enough to start it normally, then try a Windows 10 Refresh: https://www.howtogeek.com/265054/how-to-easily-...
5. If Safe Mode doesn’t work or help stabilize things then return to Advanced Troubleshoot options. Next try Command Prompt to run through Windows 10 Install Integrity Checklist (above link) repair commands including sfc /scannow, DISM, a full Disk Check, or return to Troubleshoot options to Reset Your Windows 10 PC.
6. Better yet do the vastly superior Clean Install Windows 10 following the steps in this link to delete all partitions down to Unallocated Space to get it cleanest: http://answers.microsoft.com/en-us/windows/wiki...
7. There is a step to Rescue Files from the booted media Command Prompt first: http://answers.microsoft.com/en-us/windows/wiki...

Feel free to ask back any questions and keep us posted on how it goes.

Answer 3

Really Sorry you're so upset Greg, but I'm afraid you clearly don't understand this problem.

You provided a number of solutions which, to somebody who understands what is going on, are clearly irrelevant. (I've got 30 years experience developing Operating Systems, device drivers, filesystems, etc. I'm the prime developer of an RTOS with around 1 billion units in the field....)

For example: One of your solutions was the usual bootrec /fixmbr stuff.

Had you read, and understood my post and if you understood anything about what's going on, you'd know that my computer is UEFI boot, and that stuff it totally irrelevant - on top of the fact that its got as far as loading winload.efi and is **way** past the point at which MBRs and boot records are going to be of any use. I also told you that it was booting bootmgfw.efi OK and that in turn was loading winload.efi - which again is *way* past any of the bootrec stuff.

For example: You told me how to make some installation media.

This is not a solution. It's a diagnostic tool. Further, since my post clearly showed me modifying the filesystem offline, it's obvious that I already had some other means of booting into a recovery command tool. But the key point here, is this is not a solution, and it certainly doesn't answer the questions I asked.

For example: You told me to run a surface scan on my disk. Now that's a good waste of several hours since I already told you the disk is working fine.

For example: You told me to run safe mode. Had you read and *understood* the original post, and you knew your stuff, you would have known that the boot process isn't getting as far as being able to select safe mode. Safe mode simply selects a different control set in the registry - if you don't get that far in the boot process, then clearly you can't select safe mode.

But worst of all, you told me, and thousands of others to:

"Better yet do the vastly superior Clean Install Windows 10 following the steps in this link to delete all partitions down to Unallocated Space to get it cleanest"

Did it ever occur to you that I may want to keep the data on the disk, or the installed applications?

For heaven's sake!

It's amazing how so many issues in Windows can only, apparently be solved by, "reinstalling windows". That's a true measure of the reliability of an OS isn't it? Customers really, really, don't want to re-install Windows every time Windows corrupts itself. They want an OS that is reliable and never does that in the first place!

Are there any *true* experts on here with detailed knowledge of the boot process, and in particular, working knowledge of the mechanisms by which the boot process can generate INACCESSIBLE BOOT DEVICE at the point I've described in the original post?

Or are there any better forums, where real experts live, rather than people telling you to reinstall windows and fix MBRs all the time? I suspect I'm wasting my time here! :o)

Answer 4

That's a really disappointing reply.

You haven't even come close to answering the question, or helping in any way, to the point where I'm wondering if you've even read, let alone understood  what I've said. Some of your solutions are clearly not relevant, and if you think they are then you have no understanding of Operating Systems and the boot process.

All you are doing is obfuscating the issue with a whole pile of useless, "try this", "try that" type solutions that, frankly will never work in a million years.

I've described what I've done to diagnose where, roughly, in the boot process things are going wrong. Somewhere after winload.efi loading the kernel (ntoskrnl.exe), the HAL, (hal.dll) and the registry's system hive, but before smss.exe is loaded.

So what happens around this point, in detail, to generate the INACCESSIBLE BOOT DEVICE stop?

How does the boot process decide which driver to use to talk to the disk? What registry entries does it look at in doing this?

If you don't know, leave it to somebody who does.

Please, please, please do not post random troubleshooting "guesses" that are totatlly useless, and sound like a broken record.

Answer 5

Slug -

Strange because I was thinking the same thing when I read through all of the utterly useless things you had tried.  So I gave the fixes which work for everyone else on a very well known issue here lately, only to have you fly off the handle and insult a Moderator as though you're begging to be unceremoniously thrown out . If you think I'm not serious, just try me.  You don't talk like that to anyone here, and certainly not me.  I help people by the tens of thousands in forums and everyone who cooperates and is polite and appreciative gets it fixed.