Cheers for the help guys.
It wasn't a Beta version, it was the OEM version that came with another computer. Obviously I can't activate the same copy twice, and the fact that it's OEM rather than retail will probably cause problems...?
I would like to avoid a clean install as I've spent ages getting all my other software installed etc. Just want to activate what I've got now, and make it all above board
Is it just the Product Key that makes a copy of Windows an OEM copy?
Will any Windows 7 Professional Product Key work as long as it's legit?