Security Update KB5074109 is causing my computer to not boot.

I can try what you suggested above on Saturday when the office is closed however the Windows Update is what is causing the corruption. Do you have an explanation for why it boots fine without the update?

Hi, thank you for replying. The error means there is a corrupted system file. Just to confirm, have you done the steps above? And do you still have the same issue?

That would not explain why it boots fine prior to the update. It is the update itself that is corrupting the boot sector.

Hi, I'm Bernard, a fellow Windows user. I'm happy to help!

You are correct, it seems that there is a corrupted boot configuration. In this case, I recommend using Windows installation media in USB to repair the issue. To do that, kindly follow the steps below:

Note: We need another PC and a USB drive of at least 8GB, and make sure there are no files inside, as it will reformat the USB. Once you have that, kindly follow the steps:

Step 1: Create Windows 11 installation Media

Go to this link: https://www.microsoft.com/en-us/software-download/windows11

Scroll down and under "Create Windows 11 Installation Media" click "Download Now" then run the Media Creation Tool (the downloaded file)

If you agree to the license terms, select Accept.

On What do you want to do? page, select Create installation media for another PC, and then select Next.

Select the language, edition, and architecture (64-bit or 32-bit) for Windows 11.

This table will help you decide which edition of Windows 11 you’ll choose:

On Select which media you want to use, click USB, and save it to your USB drive.

Once done, do the repair kindly follow the steps below:

Insert the USB into the affected PC

Start the PC, and if you see “Press any key to boot from DVD,” do so. If you don’t see the message, you might need to change the boot order in your computer's BIOS settings so that it first starts from the DVD or USB.

When you see the Install Windows page, tap or click Repair your computer to start the Windows Recovery Environment.

In the Windows Recovery Environment, on the Choose an option screen, tap or click Troubleshoot.

Tap or click, advanced options, and then click on Startup Repair.

The issue you're experiencing with the "Inaccessible_Boot_Device" stop code (0x78) after installing the Security Update KB5074109 could be related to several factors. Here are some steps you can take to troubleshoot the problem:

1. Boot into Windows Recovery Environment (WinRE): You can do this by using the installation media or recovery drive. Once in WinRE, select Repair your computer and then choose Troubleshoot > Advanced options > Command Prompt.
2. Check Disk and System File Integrity: Run the following commands in the Command Prompt:

      chkdsk /f /r C:
      sfc /scannow /offbootdir=C:\ /offwindir=C:\Windows
   

   Replace C: with the appropriate drive letter if your OS is installed on a different drive.
3. Verify Boot Configuration: Use the bcdedit command to check if the Boot Configuration Database (BCD) has the correct entries. You can also try to rebuild the BCD using the bcdboot command:

      bcdboot C:\Windows /s R: /f ALL
   

   Make sure to replace C: and R: with the correct drive letters.
4. Rollback the Update: If the issue persists, consider uninstalling the update if possible. You can do this from the WinRE by navigating to Troubleshoot > Advanced options > Uninstall Updates.
5. Check for Hardware Issues: Although your BIOS shows both hard drives functioning, ensure that there are no hardware issues by checking connections and running diagnostics if available.

If these steps do not resolve the issue, you may need to consult with Microsoft support or your hardware manufacturer for further assistance.

References:

• Advanced troubleshooting for Stop error 7B or Inaccessible_Boot_Device