Update February 11, 15:27 EST: A Microsoft spokesperson told BleepingComputer that the issue is caused by users not fully deploying the latest SHA-2 enablement packages.

We investigated and determined that some users encountered issues after attempting to deploy SHA-2 signed updates without fully deploying the latest SHA-2 enablement packages. For more information and step-by-step guidance, please refer to our support article: https://support.microsoft.com/en-us/help/4472027/2019-sha-2-code-signing-support-requirement-for-windows-and-wsus.

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Windows Server 2008 servers will no longer boot if prerequisites aren't installed before applying the out-of-band KB4539602 update released by Microsoft on February 7 to patch a wallpaper bug.

After being deployed on machines running Windows Server 2008 or Windows Server 2008 R2, the boot file will be deleted and the servers will no longer boot according to user reports, with dozens of servers being unable to boot as a result.

Windows 7 computers are also affected by this problem as users report having their machines rendered unbootable after installing KB4539602.

This issue is caused by older versions of SHA-2 signing and servicing stack updates on the affected devices because they were removed by admins before applying KB4539602 or because the servers weren't fully updated before installing the update. Another possible explanation is an older version of those updates being installed on the impacted devices.

As explained by Microsoft on KB4539602's entry, the following updates need to be installed as prerequisites (they should be offered automatically through Windows Update):

To make sure that these two updates are correctly installed on Windows 7 Service Pack 1 and Windows Server 2008 R2 Service Pack 1 devices, you also have to restart the computer after applying them.

Restarting the device before applying Monthly Rollup, Security-Only Update, Preview of Monthly Rollup, or stand-alone updates is also advised to make sure that it's fully patched.

KB4539602 is an optional update so you can also completely ignore this update if you don't want to have any additional issues to fix on devices running end-of-support operating systems.

Unofficial fixes

While Microsoft doesn't provide a fix for customers who get their servers unable to boot after a failed KB4539602 update, Windows admins came up with two unofficial fixes to revive Windows Server 2008 servers that won't boot:

Go into Recovery, find the drive letter for the Windows installation and run the following command:

dism.exe /image:C:\ /cleanup-image / revertpendingactions

1. Boot into Recovery.

2. Copy winload.efi and winload.exe from a backup or another 2008r2 installation to C:\windows\system32.

3. Reboot the machine.

Fixes for bugfixes

Windows 7, Server 2008, and 2008 R2 reached their end of support on January 14, 2020, and will no longer receive software updates, security updates or fixes according to Microsoft (1, 2).

After the last free Monthly Rollups released for these EoL operating systems broke some of the desktop wallpaper functionality after January 14, Microsoft released the KB4539602 stand-alone update to fix the wallpaper bug three days ago.

Some Windows 7 users are also reporting that they can't shut down or restart their computers and Microsoft told BleepingComputer that the issue is under investigation.

Now, Windows Server 2008 and Windows Server 2008 R2 customers find that their servers are being rendered unbootable after installing the wallpaper bug fix update.

More updates for Windows 7 and/or Windows Server 2008 might soon be released by Microsoft to fix the wallpaper bug fix, even though both OSs reached their end of support almost a month ago.