I was finally able to download two Windows 8.1 upgrades from Windows 8. I first ran all of the 63 Windows updates from the settings charm screen, then I went to the control panel and downloaded and installed 8 more "important" updates indicated there,
next I downloaded 1 "optional" update in the control panel, and finally I downloaded and installed the suggested update from the Windows Store download page so the download would begin. After four update sessions (63+8+1+1), I clicked on the tile in the Windows
Store screen and the download began after 16 hours of repeated failures. I repeated this sequence for my second Windows 8 computer which took about four hours, and it started to downloaded immediately and took some two hours over my Comcast connection. I
hope your success comes more quickly with this suggestion.