A number of users on Microsoft’s Community forums reported that there’s a problem with KB4103721. The Windows 10 KB4103721 is causing black screen and the system fails to boot. The only workaround which works for most of the users is to restore the system to the previous version of Windows 10.
While the first cumulative update for Windows 10 April 2018 Update (version 1803) includes bug fixes for the reported issues, it appears that there’s a bug in KB4103721 which is bricking PCs and preventing them from booting. It is, however, worth noting that not all systems are impacted.
There’s indeed a problem with this cumulative but it’s hard to determine a fix or the pattern at this point. In most of the cases, restoring the PC to the previous version of Windows helps and the PC finally boots to the login screen.
While several users have confirmed the bug on Microsoft’s Community forums, the software giant hasn’t acknowledged the installation issues yet.
Recover PC from the black screen after installing Windows 10 KB4103721
While the official workaround is not available at the moment, most of the users have managed to fix the installation issues by restoring the system to a previous point or downgrading to Windows 10 Fall Creators Update (version 1709).
You can only restore your PC to the previous version of Windows if you haven’t touched the windows.old and $windows.~bt folders after the upgrade.
The recovery process basically takes your PC back to an earlier point in time. Microsoft says that it is generated every time you install a new Windows update or driver. While restoring won’t affect your personal files, but the process will remove the apps, divers, and updates that you installed after the restore point was made.