calibre's architecture

Hello all,

I've been using Calibre for quite a while very happily. Something happened recently which has caused my entire Calibre library to appear on the desktop in 300 or so separate folders (this is Win 10 I'm using). As you can imagine, this is very awkward. When I tried to move it to a more reasonable place Calibre stopped finding my books. Where should the library be so that Calibre can find it and I don't have 300 or so folders cluttering up the desktop?

Thanks for any suggestions.

Norman