⚠️ Microsoft Investigating Boot Failure Issues in Windows 11 (Version 25H2)
Microsoft has confirmed it is actively investigating a serious boot failure issue affecting Windows 11 versions 25H2 and 24H2, following widespread reports from users after installing the January 2026 security update (KB5074109). What was meant to be a routine Patch Tuesday update has instead caused critical system instability, leaving many devices completely unusable.
🖥️ What Exactly Is Happening?
After installing the January 13, 2026 update, affected systems are experiencing:
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🔁 Boot loops (PC keeps restarting)
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🖤 Black Screen of Death
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🚫 UNMOUNTABLE_BOOT_VOLUME error
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❌ Failure to reach the Windows login screen
In many cases, users report that their systems fail to boot immediately after restart, even on physical (non-virtual) devices.
🧨 The Update Behind the Issue (KB5074109)
The problematic update, KB5074109, was designed to:
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Deliver over 100 security fixes
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Patch multiple vulnerabilities, including zero-days
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Improve system performance and stability
However, instead of improving security, the update appears to interfere with critical boot components, triggering storage-related errors that prevent Windows from loading properly.
⚠️ This issue affects:
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Windows 11 25H2
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Windows 11 24H2
🔍 What Microsoft Is Investigating
According to Microsoft, the investigation is focused on:
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Bootloader behavior after the update
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Disk and volume mounting failures
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Interaction with certain hardware configurations
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File system corruption triggered during patch installation
Engineers are analyzing logs from affected devices to determine why Windows fails to mount the boot volume correctly.
🧑💻 Who Is Most at Risk?
The issue has been reported across:
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Home users 🏠
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Enterprise systems 🏢
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Laptops and desktops 💻
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Both SSD and NVMe-based systems
IT administrators are especially concerned because affected systems may require manual recovery, increasing downtime and operational risk.
🛡️ Temporary Advice for Users
Until Microsoft releases an official fix:
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⛔ Avoid installing KB5074109 if you haven’t yet
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🔄 If already affected, use Windows Recovery Environment (WinRE)
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🧹 Consider uninstalling the update from recovery mode
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💾 Ensure backups are available before future updates
Microsoft has not yet issued a rollback update, but guidance is expected soon.
🚨 Why This Matters
Security updates are critical—but this incident shows how even trusted updates can cause major disruptions. A failed boot means:
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Loss of access to data
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Productivity downtime
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Increased support costs
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Risk for businesses relying on Windows infrastructure
It’s a reminder that update testing and staged rollouts are essential, especially for mission-critical systems.
🧠 Final Thoughts
The Windows 11 boot failure issue tied to KB5074109 is a high-impact incident, and Microsoft’s ongoing investigation is crucial. If you manage Windows systems—or simply rely on your PC daily—this is an update you should monitor closely.
🚧 Until an official fix is released, caution is strongly advised.
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