Drupal add content bug ( You have not created any content types yet )

If your content type seems to be disappeared, maybe it's just a menu issue.

That's it ... don't disable the menu item "add content -> (content)" !

Disabling it will make impossible to you to add any kind of content. Just re-enable it (and hide if you don't want to see the navigation menu).

Sometimes there are some issue moving the "add content" item to other parent menu.

You can see the full thread here:
http://drupal.org/node/997444

This one saved me from lots of hours of fight against windmills.