It may be cached, try the following:
1. Go to Settings > System > Staff > Staff Groups. Edit your staff group, make sure you have permissions to all support items. Even if you already do, save it, it will clear the nav cache.
2. You will hopefully see the Support nav item now, go to Support > Staff, make sure your staff member is assigned. If you imported, then you may have multiple staff members so make sure all of them, or at least the ones you'll be using have access to all departments.