Did you try after deactivating your other plugins like “FooGallery” etc? Which version of WordPress are you using? There can be so many reasons like function name collisions, deprecated functions if you are using old version, any css related problem in your custom theme etc.
Why are you inserting gallery into the editor? Just create one gallery upload some photos to it and embed the shortcode in one of your posts or page to view it. Just read the user guide and try once again.
Did you try viewing the gallery in one of the WordPress’s default themes. Also try after deactivating your other plugins. If the problem persists let me know or you can mail me at [email protected] with some of your screenshots.
