@hatishbi – My first thoughts are there is some sort of conflict going on with another plugin or possibly your theme. I visited you site and do not see the nggallery.css file being loaded as it is not written in the page source.
Also, you appear to have one of the Shutter lightbox effects active but it is also not working at a quick glance.
There are no general conflicts as your plugin works correct on some pages (e.g. here) but on some (most) it doesn’t. If I insert a gallery via shortcode [nggallery ] everything’s fine, looks like the .css is not loading anymore if i don’t trigger it?
Strange thing. I’m using the latest releases of WP (3.7.1) and NGG (2.0.33), it worked like a charme in the last 3,5 years until the latest updates.