I didnt go anywhere near the preview version. I am using Windows 8 Pro with Mediacenter. I ran all the updates, did a clean boot, and ran the update through the Microsoft Store.

Windows 8.1 upgrade has been a total debacle for me.

My system is a custom build and there are people with both OEM's and custom builds having major issues.

Before anyone attempts the 8.1 upgrade, run windows backup and create a system image. It will likely take some time and eat hard disk space (place on an external or secondary drive), but it's worth it. Make sure you have your original windows 8 media available since you cannot run an image restore in 8.1 for a windows 8 image. You can also create a windows 8 recovery flash drive or cd before you start using the built in tools.

If you really want to proceed, make sure you do a clean boot or at least disable EVGA precision, Logitech Software, and anything else non OS related in your startup. I was getting a similar error as someone above and it was resolved after disabling a few pieces of software. Either Steam, EVGA Precision, or Logitech was the culprit for me. Save yourself the hassle and make sure the system starts clean the first time you attempt the upgrade to 8.1.

Unfortunately the above poster who claimed the 8.1 upgrade was like a service pack is dead wrong. This is like an OS upgrade. I have never seen a service pack leave behind a windows.old folder. I poked through mine a bit and it left behind about 14 gigs worth of crap. While this folder is far from difficult to remove, you have to go into disk cleanup, "remove old system files or operating systems" to remove it. Regular users may not even know it exists and those that do wont likely figure out how to remove it since you cant simply delete it using the regular delete function. There is another folder left behind on the root of C: that contains the files for the upgrade and they look an awful lot like a windows OS upgrade image package.

In the end I had to revert back to a windows 8 system image. Im giving 8.1 more time to mature. I was able to get 8.1 working but there are numerous Nvidia and Intel display driver issues that rendered my display adapter useless. I could not get drivers to install for either the intel HD4000 or Nvidia GTX465.