Calibre not assigning icons to books

I lost all icons associated with ebooks, after formatting my machine.

I have since tried converting files - AND - opening files in the Calibre reader - and this has NOT assign an icon to the ebooks in the file. (usually .epub but also mobi and others).

How can I get Calibre to assign a file type icon to the ebooks files?

If this is a windows (vista) problem - how can I fix it?

Thanks!