another think: while playing with the not-showing slideshows (cased by the Contact Form 7 plugin), I have deleted the slideshows, removed the Slideshow plugin, reinstalled it, and voila: the deleted slideshows still work! [I mean the pages with the old (deleted) slideshows' IDs references show the old slideshows, despite tha fact they have been deleted.] Which is actually, in my case, great! :-)
The think is that I don't see them in the admin menu in the Slideshow section. How can I get them back in the list so that I can edit them?