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
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.