Restoring library after re-install of Windows

Hi,
I've recently changed from 32 bit Windows to 64 bit - wiping the HD in the process. I backed up my Calibre library to a pendrive using Calibre's Save to Disc. Having now re-installed Calibre (64 bit version) I cannot get it to recognise the old library.
I've tried using 'import data' but get the message: No exported data found in... <filepath>
Tried 'Copy to Library'>Choose Library by path and get 'No books selected' (even though there are 1500 of them)
I've tried designating the folder to Automatic Adding under Add Books but this didn't work either.
I've tried Restore Database but all that does is restore the new Calibre database, which is empty.
I've tried Switch/Create Library but that wants me to select an empty library as a new location - not what I need at all.
Looking around on this forum it seems that the initial backup I did didn't copy the metadata.db file, which is why the new Calibre isn't reading it. But each book has its own metadata, I just need to get Calibre to read it somehow.
I'm no expert in the guts of Calibre or the command line stuff so any ideas about what else I can try would be gratefully received. :help:

Thanks, Chris