domain mapping, menu item not available in tools

Hi:

My multisite installation is not working. I cannot access the created sites, only the main site and the network. Also domain mapping option in tools menu at main site is not available.
When I try to sign up and create a site, as a not-logged-in user my sites domain name does not show up in the create new site dialog. In other words, if I am trying to create a site named sitename in http://www.mydomain.com, where it should read:
(Your address will be http://www.mydomain.com/sitename.)
reads instead:
(Your address will be /sitename.)
see screenshot.

Thanks!