Suddenly the Slideshow does not show the photos anymore

What theme are you using, is the slideshow part of your theme or a plugin? link to your site?

https://codex.www.ads-software.com/Forum_Welcome#Include_as_much_information_as_possible

its based on twenty twelve .. the normal slideshow. When i click in Media in the dashboard the pictures are listed but you cant see them anymore.

There is no slideshow in unmodified twentytwelve.

sorry I mean the Header…the pictures changing after some seconds.
In the dashboard the pics are listed but you cant see the prview and if you click on them there is nothing there.

I took a look via FTP. The jpg files are still there. something must be messed up with the database

So is this on the front end of your site or only in the dashboard? Have you modified the theme at all? Have you tried deactivating all plugins to see if any are causing this to happen? Can you post a link to your site?