"Couldn't update to Windows 8.1 - 0xC1900101 - 0x40017"

I started going through the procedure, but it requires a retail Win 8.1 product key (not your Win8 key). One of the posters on that comment board, tells you a key to use but it did not work for me (LAN unplugged so it would not activate). So, I may be doing something wrong -- but, I didn't want to blow away my original Win8 install and never be able to get back to it without having to pay for a retail license Win8.1 key.

I got to about 60% of doing the install (from the small EXE which I think was just downloading it), but stopped it after I pondered all of this. Also, the application says Windows 8.1 Installation but once it gets into the license agreement and the installation, it changes to Windows 8 Installation as the title. This also scared me into thinking I was just installing Win8 over my existing installation.

Okay...  Windows Update didn't immediately find anything, but upon checking Device Manager, I found that the Intel HD Graphics had an exclamation mark, so probably it was the cause of the black screen issue... in any event, I right-clicked and told Win to locate a better driver (mistake = don't do that), and it tuned it into a generic Microsoft graphics adapter... ????

Anyways, I downloaded the latest NVidia driver for my card and (2nd mistake - should have downloaded the Intel HD one from Dell 1st) and rebooted, hoping it would re-find the Intel HD cad properly.

After the reboot... same issue as during the upgrade = black screen with cursor only.

After several reboots and playing with settings, in the advance repair process (which you get to by forcing power off a couple of times), there is an advanced boot section, which allows you to reboot and select (the old F8 way) the type of boot you want.

I booted into VGA mode 1st - no change.

Did it all over again, and went into safe mode (should have done it with networking), and finally managed to install the Intel HD Graphics F=Driver, and rebooted... straight to the desktop.

I've now installed the NVidia driver as well, and rebooted, and all seems fine again.

So, IF you are an XPS 15 (L521X) owner, I'd be downloading the 8.1 NVIdia driver, and the Intel HD Graphics Driver, and then uninstalling both, along with their drivers from Device Manager, and then WITHOUT REBOOTING, start your 8.1 upgrade.  It should go well, and at the first opportunity, install the Intel HD driver and then the NVidia one.

Back after some more testing.

Tried a chkdsk /f (yeah, I know, it says RAMDISK, but at this point, I'm willing to believe the error relates to EVERYTHING) - had some failures, restarted, went to Windows store and the update happened without me even telling it to.  I *almost* got excited something was going to happen.  Unfortunately, it's the same old story... Error on reboot.  Still have one more trick and will report back.

Has anyone tried installing from ISO:

http://microsoft-news.com/download-windows-8-1-iso-to-install-from-usb-stick/

I will try it later.

After several failed attempts, I succeeded...

Dell L521X XPS15, running a clean install of Windows8 (installed with all my data, prog's, etc about a month ago) on a 120Gb mSata drive plus a 512Gb SSD as the normal drive, and not running Intel Rapid Storage...

I went to device manager and uninstalled the NVidia Graphics Card and the drivers (ticked the box) and without restarting, did the upgrade.  I ended up with the black screen and mouse only, so turned off (with the power button).  Restarted and it went straight through the 2nd time.

Will now look for windows updates and see how it goes.