Media library not showing in lightbox mode

But it works fine when I choose Media from the toolbox, everything shows up fine. But when I try to insert a picture in a post, and choose Media Library, (in lightbox-mode) nothing shows up – just a counter saying how many items available in library. I think it has to with our host, as we did not have this issue earlier when we used a discount-host. But where can the problem be located?

Bw.