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I have at least a half-dozen Windows PCs, physical and virtual, at any given time. At least half of those machines typically run the latest Insider preview releases of Windows 11. But running pre-release code comes with its own challenges and occasional hiccups.

While running an Insider build from the Release Preview channel, I ran into one of those annoying low-grade bugs that are inevitable when you live on the leading edge. Windows Update told me a cumulative update was available for my PC, but every time I tried to install it, the update failed with a cryptic error code: 0x800f0990.

Also: The ultimate Windows 11 upgrade guide: Everything you need to know

I tried every troubleshooting step I could think of and couldn't get that update to install.

So, I moved on to the ultimate Windows troubleshooting trick, a time-tested technique that shoos away those pesky error codes like a big ol' digital flyswatter.

If you find yourself in a similar situation, feel free to break out the same big gun I did: the Windows repair installation. This is effectively an in-place upgrade using the same version that's already installed. It works for Windows 10 and Windows 11.

Also: How to upgrade your 'incompatible' Windows 10 PC to Windows 11: Two ways

This solution is considerably less drastic than a Windows reset, which wipes out your current installation and forces you to reinstall apps and restore settings. A repair installation "upgrades" your Windows PC using the same major version that's already installed. 

In the process, it restores settings to their normal state, undoing whatever tiny change is causing your current issue.

How to perform a Windows repair installation

1. Download the installer files as an ISO

An ISO file is a single compressed file that contains the digital equivalent of a Windows installation DVD but doesn't require a DVD drive. You'll find downloadable ISO files that correspond to the Windows version you're currently running in these locations:

• Windows 11 General Availability (GA): If you're running the current public release of Windows 11 (what Microsoft calls the General Availability channel), you'll find it here: https://www.microsoft.com/en-us/software-download/windows11
• Windows 10:This version will continue to be supported until October 14, 2025. Untile then, you can still get it here: https://www.microsoft.com/en-us/software-download/windows10
• Windows 11 Insider Preview: If you're living on the bleeding edge, Microsoft has your ISO here: https://www.microsoft.com/en-us/software-download/windowsinsiderpreviewiso

These files can be large (6 GB or more), so be sure you have enough free disk space to manage the download.

2. Mount the ISO as a virtual DVD drive

Double-click the ISO file to mount it in Windows as a virtual drive. In File Explorer, this mounted drive will look exactly the same as a physical DVD drive, with its own drive letter.

3. Run Setup from the virtual DVD drive

In the folder containing the mounted virtual drive, double-click Setup and wait while the Windows installer goes out and gets the latest updates. Well, not exactly the latest. As part of the fail-safe protocol, the installer downloads the next-to-last cumulative update. That precaution keeps you from getting tripped up if the most recent cumulative update is the cause of your current crashes.

Choose the option to keep all your personal files, apps, and settings, and then click Next.

Screenshot by Ed Bott

4. Return to normal

After installation is complete, restart and then check Windows Update to get the most recent cumulative update.

After I finished these steps (it took roughly 20 minutes), the update that had been giving me fits installed without any issues. 

As a bonus, another problem that had been annoying me for a few weeks was also solved. Previously, each time I restarted my PC, the infrared camera that handled Windows Hello face recognition had been unavailable, which meant I had to key in my PIN to sign in for the first time. After completing the in-place reinstall, that face recognition worked again.

Also: Microsoft blocked your Windows 11 upgrade? This trusty tool can fix that

Although it seems like a drastic step, doing an in-place repair install is a surprisingly low-key solution that has a way of solving even particularly annoying problems. If you're stumped, give it a try.

See also

Still have a Windows 10 PC? You have 5 options before support ends next yearHow to upgrade your 'incompatible' Windows 10 PC to Windows 11How to make Windows updates less annoying, in three easy steps7 ways to make Windows 11 less annoyingHow to screen-record in Windows 10 or Windows 11

• Still have a Windows 10 PC? You have 5 options before support ends next year
• How to upgrade your 'incompatible' Windows 10 PC to Windows 11
• How to make Windows updates less annoying, in three easy steps
• 7 ways to make Windows 11 less annoying
• How to screen-record in Windows 10 or Windows 11