As I don’t have access to your backend, I can only speculate.
Since you’re running 2.7 make sure that the options menu, on the left side, is expanded. Near the bottom of the list you should see WP-Slimbox2, click that and you can access options.
If that’s not the case, I haven’t a clue what’s wrong, no one else has reported this problem, but I’m open to suggestions if it’s not resolved.
If it’s still not showing up, you could take a look at your front page source, since if the plugin is loaded the slimbox JS and CSS files will get loaded, so you should see them in your install.