[Plugin: NextGEN Gallery] NG installed but doesn’t start

Hi!

I have just installed a NextGEN plugin.
I can customize the settings, I can upload gallery and see the photos in manage gallery function.
But when I post a single photo or a gallery, the NG gallery plugin doesn’t show up when clicking on the photo.
Only the browser opens the photo(s).
What can cause this?
Photos must be in albums for posting? Or can I post a gallery without albums?

Please help me!
Thanks!