Ok.
First things first, double check that the Gallery ID on the "Manage Gallery" page is 1. Sometimes when deleting and shuffling galleries, things can get confused.
Second, due to the way some plugins/themes/etc process shortcodes, a space can be the difference between "It works!" and "What's wrong??".
I'm not at work so I can't confirm for you, but according to this page there shortcodes have spaces. I seem to remember that being a requirement.
Once you've confirmed the ID, change the shortcode like so:
[ nggallery id=1 ]
Be sure to replace the "1" if you need to.
If this doesn't work, reinstalling NextGen might be a next step. It won't delete the actual images and info you've uploaded and it's a pretty quick process.
Let me know how that goes.