@Lodder I have just thought that if I copy the protostar template then I will loose all the fixes that are made in Protostar in the new Joomla version. But I guess there is not other way than either edit core file/make a backup/update/edit core files with previous changes (a bit of hassles, but keep the fixes that are made) OR duplicate the template (simple but I loose the fixes). Maybe there is a third way of doing it?

@Lodder, thanks for the side notes, I will be more carefull with overrides now (I do them sometimes, but not all the times)

Thanks so much Fari for the print-screen. I didn't know about this backend feaures. Know, thanks to you, I am protected from loosing my edits!

I have replaced in my home page {module test} (module anywhere) by {loadposition custom,test} and I have the same result: {loadposition } allow my to access my article. If I remove {loadposition}, I can't acces my website just like when I remove the module anywhere tag. (you are right, I am talking about module anywhere from NoNumber). In brief, my website need to load a module inside an article in order to work.

OK, I understand now and then everything is normal. Thanks a lot Lodder for your help!

yes, I only want to move new .css and new .php from my computer to the ftp, or to edit the existing Joomla files. So the OVH manager is the one which allows Joomla to access to the ftp. That's confusing because for Joomla to access the phpmyadmin I have to set the new password in configuration.php

Thanks Lodder! I don't thing I have created a separate FTP account because I can't connect via filezilla with the previous password and I have updated it via the OVH manager. In Global Configuration/Server/FTP Settings, "Enable FTP" is set to No. If I set it to yes, then all the fields are empty: is that normal?

I actually have a bilingual website so the redirection to /en/ is normal. I will try as you said to disable all extension one by one.

Ok I could get a bit more understanding of the issue. My home menu is a single article menu item and I change the article linked to the home menu and now I have access to my website with the debu set to off. Now the problem is that some menu items work well but other redirect me to the "website not available" page (cf print screen). Could it be that there is a bug somewhere in my Db rather than my website being hacked?