I have 3 computers, all running Windows 8 with no problems. I could not update to Windows 8.1 on any of them using the Store. Just kept repeating the download over and over with never running the installation. I was able to update to 8.1 on 2 of the computers using the ISO/DVD method as described in several places on the forum. This went smoothly. On the third computer, installation seemed to be working (went past the 100% mark), then suddenly popped up the message "Windows 8.1 installation has failed" and the installation abruptly halted. There was no explanation or error code. My question is: what causes this message? There must be a way to determine what triggers it so the problem can be corrected. I can find no log file or other clue. Maybe I don't know where to look. If anyone has the solution to this annoying problem, please let me know.