new topics are not displayed in forums

Hi, I've been trying all day long to post a topic on a forum, but with no results. In fact if I click on the "Post New Topic" link, fill all the necessary fields, select the right forum and press the "Save" button, I'll get the new node displayed, but when I go back to the forum the topic is not listed although the node is regularly listed in /admin/content/node.
Can anyone help me, please? That's really turning me mad. Actually I'm quite a newbie with Drupal, so probably it's just a "silly" problem of bad configuration, but after having read all the project issues and googled for hours, I'm really running out of ideas!

Thanx!