>I had an old database which I zapped - then I went onto the web and downloaded a newer version onto my computer and put in in the original directory where the cdx of the old file still remains
>
>But if I try to reindex nothing happens - the downloaded file has the same fields as the original
>
>Why cant I reindex the downloded file

Depending on whether it is a free or database table differing link mechanism exist for the "automatic" index IIRC.
In your question file, database and cdx are IMO not correctly described