I am facing this problem, although I am 100% certain that I made all the required steps of converting a WP into a MutliSite, including adding the two different lines into the config.php
define( 'MULTISITE', true );
the lines are correctly put, with nothing missing (I have just made sure they are).
I see no super admin menus at all, although the my account is an admin account, and it is the first account through which I made the installation (I upgraded a current WP not installed a fresh one).
what could it be ?