Unwanted inverted posts order

Hello,
I’ve a wordpress site that have a strange anomaly from yesterday. When trying to view the main page posts this appears with inverted order, starting from the most oldest(August 2006).

I’ve not modified anything, I’ll tryed to put the strings finded in the documentation of codex.ww.wp.xz.cn and from this link: http://www.nietoperzka.com/wptraining/custom-order-of-posts-on-main-page/

like that:

(<?php $posts=query_posts($query_string . '&order=desc');
if (have_posts()) : while (have_posts()) : the_post(); ?>)

in the index.php to put the posts in the desc order, but nothing. Also tryed to play with other strings or to search a plugin for date management but this bug won’t give up.
Sounds like an ID sorting starting from the first ending with the last…

I’m not running any new plugin, not modified the db, not changed the theme and not upgraded the wp version… This site are working greatly from August 2006.

Why now I have this situation, and how can I fix that? An upgrade can solve that?
Thanks in advance and sorry for bad english.