9 times out of 10 it’s because one of your javascripts is crapping out and thus taking all the others with it. Disable all plugins excepts for WP jQuery Lightbox and see if it makes a difference.
I ruled out all my plugins, but this has also occurred for me. The lightbox is simply not loading anymore. Using Firefox 17.0.1 by the way.
vind your theme does not output the lightbox script. This happens when your theme does not call wp_footer and wp_head as it should.
http://codex.wordpress.org/Function_Reference/wp_footer
http://codex.wordpress.org/Plugin_API/Action_Reference/wp_head
Ouch. Turns out I messed up my footer when doing customizations to my child theme. I think I got it covered now by copying the closing tags from the parent footer.php. At least the lightbox is working again now, so thanks for pointing that out.
I tried mine but still no luck.
Today i have find out the same weird thing that suddently WP jQuery Lightbox stopt working without changing header.php or footer.php and without new plugins for many months.
Maybe some plugin updates were evoking this.
Try with changing the position (line in code) from <?php wp_head(); ?> in the header.php file.
I have put it a little bit higher in the code and WP jQuery Lightbox works again. Keep <?php wp_head(); ?> in between the <head> tags.
Thank you vind! I’ve been going crazy for days trying to figure out why my lightbox suddenly wasn’t worried when I stumbled upon your answer. I, too, messed it up when I made a change to my footer! Thanks for restoring my sanity.
Can someone have a look at mine and see why its not working? (WP 3.6.1, WP jQuery Lightbox 1.4.5)
http://www.kalaharigraniet.co.za/caesarstone/