Problem solved!

In case anyone has the same issue, the problem was a line of code, in this case I had put this Facebook code in header.php:
<script type=”text/javascript” src=”http://ajax.googleapis.com/ajax/libs/jquery/1.5.2/jquery.min.js”></script><script src=”http://connect.facebook.net/es_ES/all.js”></script&gt;

This code was generating conflict not only with the toggle menu, but also with de search button and the pagination in the blocks (when I pressed the arrows nothing happened).