URGENT! Upgraded from 2.2.2+ to 2.6.2+ and have many problems

I upgraded a working Moodle installation from 2.2.2+ to 2.6.2+, having zero errors in the upgrading process, but afterwards I found many problems:

1. All images got broken (all icons are broken images and point to things like http://cursos.webizando.es/theme/image.php/standard/core/1399198647/i/info which is something not found.
2. Many admin options do not work and cannot be accesed. For example, most of the site admin options do not work and nothing happens when you click on them (they are not even highlighted as links).

I have reviewed the Upgrading and Install processes in Moodle Docs, and also the Installation FAQ and teh Upgrading FAQ, but I find no solution to these problems. I also tried to find solutions searching in the forums and in Google, but found nothing. 

Can anyone help me with this? It is urgent to fix it, since it is a production server. I added an image from my admin view in Spanish (sorry I cannot even change the language to English in the Moodle server).