Yes, after having powered off and restarted the computer, Win8.1 has been automaticly restored. The drivers cannot be the source of the problem, because the upgrade failed regardless of the previously installed third party drivers. I tried to do the upgrade just after having done a clean install of Win8.1 (without the installation of any third party drivers) and after having installed them all. The result was always the same.
just in case you didn't already try: unplug all hard disks you don't need (all but your windows hdd) this solved my upgrade issues ~2 months ago when I tried to upgrade from one win10 build to another while also having win8.1 on another hdd, maybe they still didn't fix this
Yes, this is what I did, but the result was always the same. I tried the upgrade with different images, USB Flash Drives and different system drives (all of them were SSDs), but the result was always the same: The upgrade ended at 23, 24 or 25% of the procedure.
I had similar problem twice! Both time I need to let the machine run and finally it installed correctly. Once it took more than 7h for to be finish. That was on an DFI LanParty MB 6 years old!
your win 8.1 installation source isn't modified in any way? wierd stuff can happen when using isos with integrated updates/disabled services/etc
No, my Win8.1 source was the original ISO file incl November update, which I had downloaded from Microsoft.
:/ If you're going to do a clean Windows 10 installation later and only want to upgrade to keep the activation you could try to upgrade from Windows 7 to test if the faulty driver comes with Windows 10.
What lets you think, that a faulty Win10 driver is responsable for the upgrade failure? The hang happens within the first part ("copying files") of the upgrade, whereas the hardware detection and driver installation happens within the next section. By the way: I had no problem to get Win10 clean installed onto my Z97 system. So there should not really be a driver problem.
I tried to upgrade from Win8.1 to Win10 by running the Setup.exe of a proper Win10 Build 10240 image.
Try this: Open Command Prompt (Admin) Type the following command (without '') : " rundll32.exe pnpclean.dll,RunDLL_PnpClean /DRIVERS /MAXCLEAN " Hit Enter on your keyboard Exit command prompt. Restart and try to update again through USB boot or double clicking the setup.exe from your USB drive and install/upgrade to W10 again.