wordpress gallery plugins not working

So I am trying to set up a gallery with a decent lightbox plugin.. I've tried several of them, but none of them is working.. Even though I follow the documentation and setup, it still shows the images just as before - single, plain ugly images.

Is there something I have badly configured in my WP settings? I have no idea where to go from here.. Any ideas / suggestions ? Thank you.

//edit: just tedted, on my other WP site it works ok. Now I don't know if it's the WP version issue (the other site is different version of WP, or perhaps the custom theme?

Edited April 23, 201511 yr by mccloud