Windows 11 26H2 Failed to Install on Windows 10? 8 Ways to Fix the Upgrade

Trying to upgrade from Windows 10 to Windows 11 26H2, but the installation keeps failing? Incompatible hardware, outdated drivers, insufficient storage, damaged system files, or interfering software can cause the problem. In some cases, Windows 11 starts installing but eventually rolls back to Windows 10. In others, the installation may stop with an error code such as 0x80070070, 0xC1900101, or 0xC1900208. This guide explains what to check when the Windows 10 to Windows 11 26H2 upgrade fails, along with the fixes you can try before considering a clean installation.

1. Check Whether Your PC Meets Windows 11 Requirements

Before troubleshooting the upgrade, make sure your Windows 10 PC meets the minimum Windows 11 requirements. Your device needs a compatible 64-bit processor, at least 4 GB of RAM, 64 GB of storage, TPM 2.0, and UEFI firmware with Secure Boot capability.

The easiest way to check compatibility is Microsoft’s PC Health Check app.

1. Open PC Health Check.
2. Select Check now under the Windows 11 eligibility section.
3. Review the result and fix any reported compatibility problems.
4. Try the Windows 11 26H2 upgrade again.

If TPM 2.0 or Secure Boot is disabled but your PC supports them, you may be able to enable them in the UEFI/BIOS settings.

Also check your Windows 10 version by pressing Win + R, typing winver, and pressing Enter. Windows 10 version 2004 or later is required for Windows 11 upgrade.

If the PC Health Check app reports an unsupported processor or other hardware requirement, fix that compatibility issue first. Windows Update troubleshooting won’t fix a hardware requirement the PC doesn’t meet.

2. Check Your Internet Connection

Windows needs a stable internet connection to download Windows 11 installation files and complete parts of the upgrade process. If the connection drops during the download or preparation stage, the installation may fail.

Try these steps before starting the upgrade again:

• Restart your router or modem.
• If possible, connect the PC using Ethernet instead of Wi-Fi.
• Avoid using a metered connection while downloading the upgrade.
• Make sure other devices or downloads are not heavily using the connection.

Third-party antivirus programs, firewalls, and VPN software can sometimes interfere with Windows setup. Disconnect from VPN and temporarily disable or uninstall third-party security software before trying the upgrade again.

3. Free Up Storage Space

A Windows 11 feature upgrade needs free space to download installation files, unpack them, create temporary files, and complete the upgrade. If the system drive is nearly full, the installation may fail or roll back to Windows 10.

Check the available space on your C: drive in File Explorer > This PC. If storage is low, remove unnecessary files before trying the upgrade again.

You can use Windows’ built-in cleanup tools:

1. Open Settings > System > Storage.
2. Select Temporary files.
3. Remove files you no longer need.
4. Empty the Recycle Bin if necessary.
5. Restart the PC and try the Windows 11 26H2 upgrade again.

If you see error 0x80070070, check available storage first, as this error on devices with insufficient storage space on the system drive.

4. Run the Windows Update Troubleshooter

If Windows Update is having trouble downloading or preparing the Windows 11 upgrade, run the built-in Windows Update troubleshooter. It can detect common problems with Windows Update components and related settings try to fix them.

On Windows 10:

• Open Settings > Update & Security > Troubleshoot.
• Select Additional troubleshooters.

• Choose Windows Update and select Run the troubleshooter.
• Follow the instructions and apply any recommended fix.
• Restart your PC and check for updates again.

If the troubleshooter finds and fixes a problem, try the Windows 11 26H2 upgrade again.

5. Reset Windows Update Components

If the Windows Update troubleshooter doesn’t fix the problem, the update cache or related services may be damaged. Resetting the Windows Update components forces Windows to rebuild the update cache.

Open Command Prompt as administrator and run these commands one at a time:

net stop bits
net stop wuauserv
net stop cryptsvc

Then rename the folders used by Windows Update:

ren %windir%\SoftwareDistribution SoftwareDistribution.old
ren %windir%\System32\catroot2 catroot2.old

Restart the required services:

net start cryptsvc
net start bits
net start wuauserv

Restart your PC after running the commands. Then open Settings > Update & Security > Windows Update and check for updates again.

Windows will create new SoftwareDistribution and catroot2 folders automatically when the related services start working again.

6. Repair Corrupted Windows System Files

Damaged Windows system files can cause an upgrade to fail even when the PC meets all Windows 11 requirements. You can use DISM and System File Checker to repair the existing Windows 10 installation.

1. Right-click Start and select Windows PowerShell (Admin) or Command Prompt (Admin).
2. Run this command:

DISM /Online /Cleanup-Image /RestoreHealth

Wait for it to finish. Then run:

sfc /scannow

SFC checks Windows system files and replaces corrupted files when possible.

After both commands complete, restart your PC and try the Windows 11 26H2 upgrade again.

If DISM or SFC reports it couldn’t repair some files, don’t repeatedly run the Windows 11 installer. Continue with the next troubleshooting step first.

6. Disconnect Unnecessary Devices and Check Drivers

External hardware and incompatible drivers can cause Windows Setup to fail, especially when the upgrade gets partway through and then rolls back to Windows 10.

Before starting the upgrade:

• Disconnect unnecessary USB drives and external storage.
• Remove printers, scanners, and other peripherals you do not need.
• Check Device Manager for devices showing a warning icon.
• Install available driver updates from your PC manufacturer’s website.

Pay close attention to storage, chipset, graphics, and network drivers, as issues with these drivers can stop or roll back an upgrade.

After updating drivers, restart Windows 10 and try the upgrade again. If the installation previously failed with error 0xC1900101, checking drivers helpful because this error is commonly associated with driver-related upgrade failures.

7. Try Windows 11 Installation Assistant

If Windows Update keeps failing, try Microsoft’s Windows 11 Installation Assistant. It offers another way to upgrade from Windows 10 without a clean installation. Before you start, make sure your PC meets the Windows 11 requirements and that you have backed up important files.

• Open Microsoft’s Windows 11 download page.
• Under Windows 11 Installation Assistant, select Download Now.

• Run the downloaded tool as an administrator.
• Let the Installation Assistant check your PC for compatibility.
• Review the Microsoft software license terms, then click “Accept and install” to proceed with the Windows 11 upgrade.

• The Installation Assistant will now start downloading Windows 11. This process may take some time, and you can keep using your PC while it downloads.

• Once the download is complete, click “Restart now” to start installing Windows 11.

Note: Make sure your laptop is connected to the AC adapter during this process, and avoid forcing a shutdown to prevent any potential issues.

After the computer restarts and you’re back at the desktop, it means the Windows 11 installation process is finished.

8. Upgrade Using Windows 11 Installation Media (ISO)

If Windows Update and the Installation Assistant both fail, try an in-place upgrade using Windows 11 installation media. This method lets you start the Windows 11 setup directly from your existing Windows 10 installation.

• Download the Windows 11 ISO from Microsoft’s official software download page.

• Right-click the ISO file and select Mount.
• Open the mounted drive in File Explorer. Double-click setup.exe.

• Follow the Windows 11 Setup instructions.
• When asked what to keep, select Keep personal files and apps.

• Continue with the installation and allow Windows to restart until the upgrade finishes.

Select Keep personal files and apps if you want to upgrade Windows 10 without removing your files and installed programs.

If that option isn’t available, stop the installation and investigate the reason first. Don’t continue with an option that removes your apps or files unless you deliberately chose a clean installation.

What to Do If Windows 11 26H2 Rolls Back to Windows 10

If Windows 11 starts installing but eventually rolls you back to Windows 10, the upgrade didn’t complete successfully. This can happen because of a driver, incompatible software, hardware issue, or another problem detected during Windows Setup.

First, note the error code or message shown after the rollback. Then try these steps:

• Disconnect unnecessary USB devices.
• Update your important device drivers.
• Remove incompatible third-party software.
• Make sure the system drive has enough free space.
• Run the DISM and SFC commands mentioned above.
• Try the upgrade again using the Windows 11 ISO.

If the upgrade keeps rolling back, Windows Setup logs can provide more information. You can find important setup logs in:

C:\$WINDOWS.~BT\Sources\Panther

Look for errors in the logs rather than repeatedly running the upgrade without knowing what caused the failure. The specific error code can help identify whether the problem involves a driver, application, hardware compatibility, or the existing Windows installation.

Frequently Asked Questions