I have a dual-boot machine with Win10 on one partition. This morning, Windows installed a large update with the comment "your machine will restart several times". Sure enough, the update took forever, and afterwards...there's only Windows 10 left.
I haven't yet gone spelunking with a LiveCD, but Win10 updates have been known to nuke entire partitions, not just the bootloader. Time will tell...
For what it's worth, the Windows update history shows: KB 3176937, 3176935, and 3193494. This would appear to be a group of updates that lead to "Windows 10 version 1607".
This week, Microsoft pushed out another cumulative update and reports of installation problems are widespread. While I don't know how many users are impacted, based on comments sent to me, it's certainly widespread enough that this is well beyond an isolated issue.
The update that is causing the problem, KB3194496, is not installing correctly for users. The update, when it does fail, is causing some machines to restart, often multiple times, as Windows 10 attempts to remove the failed update. Worse, after a restart, the file will attempt to install again resulting in the loop of failed install, reboot, re-install and failure again.
Some users have reported that the cumulative update did install correctly on the second or third attempt while others have said that it fails every time.
[...] Microsoft is pushing the idea that you should always patch your machine on the day the update is released as they often release security patches that fix vulnerabilities. But, until the company can get a handle on their quality control issues, such as the Anniversary update breaking millions of webcams, it feels like every time you run Windows update you are rolling the dice.
Some have found a solution to their problem here.
(Score: 3, Informative) by butthurt on Monday October 03 2016, @06:29AM
Unfortunately there's no screen reader during BIOS/POST, so I can't interact with the boot menu to choose the LiveCD or USB boot options.
Waiting for the "Press F12 for the boot menu" prompt beore pressing F12 (sometimes it's Esc) takes quick reflexes. I'm not that quick, so I press the key repeatedly from the moment I turn on the computer until the menu comes up. Unless your computer detects your USB drive erratically, the menu should always be the same. If you were to go over the use of it a few times with a sighted person, you could, I would think, work out what keys must be pressed and how long to wait between key-presses.