Now, when I click on any album, it start the slideshow and loads the thumbs, but they're all behind a big black layer and I can't click on anything to start the slideshow or select any thumb.

Any clues?

I tried to activate and deactivate some plugins with no success. Which plugin is responsible for this?

How about some details and/or a link? What theme (no official theem starts a slideshow if you click on an album)? Errors in the server log? Is the /albums folder there and are there albums?