Three restarts and a ten-minute black screen: why this month's update looks broken

Restart. Restart again. Then a black screen that just sits there - no logo, no spinner - for ten minutes. A lot of people hit that while installing this month's Windows update and reached for the power button, which is the one thing you really shouldn't do.

What's actually going on: Windows is replacing the Secure Boot certificates issued back in 2011, which started expiring in June. Unlike an ordinary patch, that change has to be written into the PC's firmware, and the sequence takes several passes - stage the change, write the new certificates, then boot once using a freshly signed bootloader. Each step wants its own restart. Microsoft's phrasing is refreshingly direct: "There are multiple reboots required for the process of updating the certificates," and then the useful half, "Once the certificates are updated, you won't see these multiple reboots anymore."

The reason it's suddenly everywhere is sitting in the release notes for KB5121003, the August 11 update. It ships "additional high confidence device targeting data, increasing coverage of devices eligible to automatically receive new Secure Boot certificates" - meaning far more PCs are getting the certificate swap this month than last. One tester watched a black screen for a full ten minutes, then a spinner parked at 93%, with the whole install running past fifteen minutes.

So leave it be. Plug a laptop in before you start, pick a moment when you don't need the machine, and give it considerably longer than feels sensible before deciding it's frozen. Cutting the power halfway through a firmware write is how a slow update turns into a dead PC.

If an update genuinely does jam - stuck for an hour, or failing and rolling back every time - that's what Tendvane's Windows Update repair wizard is for, and check-for-updates will tell you straight whether August's patch actually landed.