"Windows 8 Installation Failed"

Just bought my upgrade to Win 8. It downloaded fine, but when I try and do the upgrade, it goes through it's initial checks, etc, and when I get to the 'begin installation' step, it goes full screen, dark blue with "Installing Windows 8", but before it can do anything, I get a pop up error that simply says "Windows 8 Installation Failed". No other information whatsoever.

Any ideas? Tried making a DVD and installing from disk outside of Windows, but it tells me for an upgrade it needs to be run from inside Win 7.