Thanks for your reply, but maybe I was not clear in explaining: the main trouble was in the admin panel, not in the frontend. The menus in the top bar of the backend panel did not work. Strange characters appeared in the sidebar. It was impossible to do almost anything.
And it occurred right after installing the two components. As I told you, the frontend problem was solved before your reply.
Anyway, I tried again, after your reply, to access the administrator panel with other browsers. And with Firefox and Safari now it all seems to work correctly. But:
1) I need to install Admin Tools and Akeeba Backup (pro versions both, I am a subscriber) on the site. How can I do this avoiding to have the same problem I experienced before? Could this be a problem related to component/Jomla/Php versions compatibility?
2) Still I cannot work on Opera in the backend. How can I solve this?
Thanks in advance for your reply