Installation fails after first step

I'm running Win8 CP 64-bit.

I ran the Upgrade Assistant program & purchased my license/key.
I cancelled the download as I already have the RTM from a few months ago on a bootable flashdrive.

I boot from the USB drive, choose my location from a standard looking Microsoft dialog, click Install.
Oh, I chose to keep my current programs. Don't really want to track down and customise about 30 odd extra programs if that can be avoided.

It then says to remove the install media & restart the computer as normal. It says that setup will continue after that, but it doesn't.

Note: I edited the cversion.ini so it will upgrade over my version.

How can I check the reason? Is there a windows setup log somewhere?

read this article, it should answer your question:

Bloggers show how to upgrade Windows 8 previews to RTM - Computerworld

Thanks, but seen it and done it. That's why I mentioned I edited the cversion.ini file.

Reinstall your old OS, using the backup image you made before upgrading to Windows 8 CP 64-bit, than upgrade from there.