If you are trying to upgrade to Windows 10, but keep getting the cyptic error code of 80070002, it could be time to open your box and unplug some cables.
Upgrading to Windows 10 is a mostly painless process, when it finally starts to kick into gear, but to reach that point can be somewhat be frustrating.
If you are the sort of computer user that has old Windows installations lying about on various drives because, for instance, an SSD purchase gave you an opportunity to blow away years of built up Windows craziness and start afresh with a new install, then the upgrade process may not go as smoothly as hoped.
In my own upgrade experience from the weekend, everything was going swimmingly until the computer rebooted, and when the upgrade should have started, the screen flickered a couple of times, a restart occurred, and I was returned to my Windows 8.1 environment to start again.
When the download for the upgrade came in at approximately 2.5GB, it's not a process you want to do too many times, especially when you keep getting the same error despite trying various workarounds. Therefore, if you suspect your setup may create headaches, I recommend creating an upgrade USB drive to save download heartache.
For me, I always saw the 80070002 error code, and Microsoft's official explanation and workaround did not help. Fortunately, this forum post contained the answer I was looking for: Unplug all other hard drives containing a former Windows installation.
Once the upgrade started in earnest, everything behaved as it should -- until I tried to boot into Linux, that is. When I attempted to boot into my long-suffering Gentoo install, I was informed that the kernel could not find the root filesystem.
After an hour of panic and fearing that Microsoft had returned to the "land of wiping drives for little or no reason", the eventual cause was found to be Windows adding an extra partition during the upgrade. Consequently, the partition entries in GRUB needed to be incremented to function as before.
Should you be upgrading Windows 7 or 8, and you have a Linux installation on the end of the same drive, do not freak out when your bootloader decides it cannot find Linux.
Having used Windows 8 and 8.1 prior to 10, there is little that has blown me away on first impressions, except for the ability to play and stream games and apps from an Xbox One over a local network -- that is a mighty cool new feature.