Can’t enter comments on (basically) default installation

I just noticed the other day that for some reason my blog will not allow commenting. Please help me figure out what’s going on.

First the basics:

• Settings -> Discussion -> Default article settings -> Allow people to comment on the article = checked (in fact, everything on that page is checked except “An administrator must always approve the comment” and “Comment author must have a previously approved comment”
• Individual blog entries are set with “allow comments” checked.

Other relevant information:

• I’m using Greening, and I haven’t modified any files in my wordpress install except wp-config.php (username, password added), wp-content/themes/greening/footer.php (inserted a creative commons license) and wp-content/themes/greening/index.php (entered the following code:

  <?php if (is_home()) {
       query_posts('showposts=1');
  } ?>

  right before the <?php if (have_posts()) : ?> line)

• I’ve got askimet activated with a valid key, but of course it has nothing to work with since comments aren’t being accepted on any page

I have another blog installed using a different theme, but with (as far as I can tell) all settings identical, and it allows comments just fine (anonymous, OpenID, username/password all work).

Please tell me what I am doing wrong! Thanks in advance for all your help!

jeff