I used the add data button once to add a basemap. i must have faulted with something along the way because since then i haven't been able to do that again. When I click the add data menu, the 'add basemap' option is not selectable same as the online basemaps
I would recommend taking a close review of the following link with your IT department. This should help you narrow down where the issue lies.
If you still can't add basemaps after a thorough review of that article, feel free to give us a call at Esri Support to log a case - we can take a look with you!