First of all, thanks for trying to help me!
The URL of my site is codegenerationcenter.com
Let me summarize my problem. The page to list/edit categories: http://codegenerationcenter.com/wp-admin/edit-tags.php?taxonomy=category
shows the "slug" and "description" fields of all categories but not the name that appears as if it was an empty string. Same happens if I edit a category. The edit form shows all fields filled except the name one that it's empty (even if I remove the slug and write a name for the category, the name will be copied to the slug but the name field will show empty again afterwards).
Surprisingly, I've checked the database and the table wp_terms show the name as correctly stored.
Maybe as cascade effect, I'm unable to assign the default category in settings->writing since no dropdown list is empty. I have the same poblem with post tags. Maybe unrelated but could this also affect the loop functions? In the home page only one blog post is shown.
I'm running wordpress 3.1.3 in Linux.