Just finished installing the August cumulative update KB5121003 on Windows 11, only to find your PC stuck on the boot logo after restarting; or you finally get into the system, but games crash or blue-screen as soon as you launch them. If you're going through this, you're not alone—this is the real situation many users encountered in the August 2026 Patch Tuesday update.

KB5121003 is a cumulative update Microsoft pushed to Windows 11 24H2 and 25H2. After installation, the system version numbers rise to Build 26100.9168 and 26200.9168 respectively. It fixes more than 420 security vulnerabilities in one go, and Microsoft even recommends completing the installation within 3 days. Its security value is beyond doubt. However, on some devices, this update has caused installation failures, game crashes, system stuttering, and even blue screens, affecting models from HP, Dell, and other brands.

This article will help you determine which type of problem you're encountering and provide troubleshooting steps from simple to complex. Before proceeding, be sure to back up important data, and strictly follow the steps for operations involving the registry and command line.

First, understand: what changes KB5121003 brings

As a monthly cumulative update, KB5121003 fixes more than 420 security vulnerabilities and is the most important Windows security patch of August 2026. In addition to security fixes, it also brings some improvements for daily use:

  • File Explorer's details view no longer uniformly displays as KB, but automatically adapts to KB / MB / GB units.
  • Windows Search supports searches with a minimum of 2 characters and enhances tolerance for spelling errors.
  • Windows Hello Enhanced Sign-in Security (ESS) begins supporting external fingerprint recognition devices, so desktops can also use hardware-isolated identity authentication.
  • Precision touchpads add new customization options for scrolling and zoom speed, and Voice Access adds background noise filtering.

However, some newly added security mechanisms also bring compatibility side effects, which is the root cause of the frequent problems that follow.

What to do if installation fails or it's stuck on the boot screen

If you encounter the message "Some operations did not go as planned" when installing KB5121003, or after restarting it stays stuck on the brand logo screen for a long time and eventually the system automatically rolls back, this usually means the update could not be successfully completed during the restart phase. Common error codes include 0x800f0845 and 0x80040154.

The recommended troubleshooting order is as follows:

  1. Confirm the system version. Press Win + R, type winver, and confirm that your system is Windows 11 24H2 or 25H2. If you're still on 23H2, you need to complete the feature update first before installing this patch.
  2. Repair system components. Open Command Prompt as administrator and run the following in order: 
    DISM /Online /Cleanup-Image /RestoreHealth
sfc /scannow
    Restart the computer after both commands show success. Only try the update again when DISM and SFC both report no issues.
  3. Reset the update cache. If the first two steps don't work, run Command Prompt as administrator and execute: 
    net stop wuauserv
net stop bits
ren C:\Windows\SoftwareDistribution SoftwareDistribution.old
ren C:\Windows\System32\catroot2 catroot2.old
net start wuauserv
net start bits
    Windows will automatically rebuild these folders, then restart and try the update again.
  4. Install manually. If automatic updates fail repeatedly, go to Microsoft's official Update Catalog website, search for KB5121003, and download the .msu file that matches your system version to install manually.

If you've tried all the above steps and it still fails, consider pausing updates for 2-4 weeks and waiting for Microsoft to release a fix before resuming automatic updates. KB5121003 involves a large number of kernel security changes, and compatibility with some hardware platforms may require subsequent cumulative updates to improve.

Game crashes and blue screens: inpoutx64 driver conflict

After installing KB5121003, some users launching games with anti-cheat features such as ARC Raiders and THE FINALS encounter EXCEPTION_ACCESS_VIOLATION errors, game crashes, or even direct blue screens. Microsoft has confirmed that the root cause is a conflict between the inpoutx64 kernel driver installed by RGB lighting control software and the updated kernel protection mechanism.

If you don't play these games, you can skip this section. If you do encounter it, handle it in the following order:

Option 1: Disable the inpoutx64 driver (reversible, recommended to try first)

  1. Press Win + R, type regedit to open Registry Editor, and first right-click to export and back up the entire related key.
  2. Navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\inpoutx64.
  3. Double-click the Start value on the right, change the value data to 4, confirm, and restart the computer.

Start = 4 means the driver is disabled. After restarting, the lighting software may stop working, but it won't affect normal system use. If you need to restore it, change Start back to its original value.

Option 2: Uninstall the problematic RGB software

If disabling the driver solves the problem, it's recommended to further uninstall the RGB lighting control program causing the conflict. Open "Settings > Apps", sort by installation time, find the recent RGB control software and uninstall it. After restarting, go to Device Manager and confirm that there are no inpoutx64-related entries under "System devices". If you want to keep the lighting effects, you can switch to open-source solutions that use whitelisted drivers, such as SignalRGB or OpenRGB.

Option 3: Uninstall KB5121003 (last resort)

If none of the above methods work, you can uninstall KB5121003 as a temporary solution. Open Command Prompt as administrator and execute:

wusa /uninstall /kb:5121003 /quiet /norestart

Or go to "Settings > Windows Update > Update history > Uninstall updates" to find KB5121003 and uninstall it. Restart the computer after uninstalling.

Important reminder: Uninstalling this update means more than 420 security vulnerabilities are exposed again. Please use this only when you've confirmed the problem is indeed caused by KB5121003 and other solutions are ineffective, and pay close attention to Microsoft's fix progress.

Daily prevention and follow-up attention

Microsoft pushed fix measures for the game crash issue in late August 2026 and began blocking the loading of related conflicting drivers. It's recommended to check and install all the latest updates in Settings so the system automatically obtains the fixes.

In daily use, developing two habits can help you reduce similar update troubles: first, before installing large cumulative updates, manually create a system restore point so you can quickly roll back if problems occur; second, pay attention to the "Windows release health" page to learn whether the current version has known issues before deciding whether to install it immediately.

If you're not sure whether the problem is caused by KB5121003, the most direct way to verify is: uninstall the update and observe whether the problem disappears. If it disappears, you can basically confirm the association; if the problem persists, you need to troubleshoot from other directions such as drivers and hardware.