everything started with a "ERROR ESTABLISHING A DATABASE CONNECTION"

Hi!
Since few days the website was down and showed the above message. Nobody modified anything, it simply started to give the error.

I followed some instructions found in this forum, and added the
define ('WP_ALLOW_REPAIR', true);
in the wp-config file.

Since then, in the attempt of loading the website
http://www.fortecarlo.com

different messages appear, like “Fatal error: Call to undefined function wp() in /web/htdocs/www.fortecarlo.com/home/home/wp-blog-header.php on line 14”

Since the WordPress version used by the website was not up-to-date, I started updating the wp-files through FileZilla, in ftp mode.

The problem is that now every attempt to overwrite the old files, results in a zero kb of uploaded file. (Of course the file stored locally was not zero kb!).
Following some suggestions found on the web and (whatever that means) I tried to:
. force UTF-8 in the charset
.expressely flag the passive transfer mode
.traceroute the website: the result was “fortecarlo.com has multiple addresses, 64 hops max, 52 byte packets”

My first question is:
1) there is an alternative way to manage remote files?
2) do you have any suggestion?

Please help me, I am really lost.
Of course if you need more details, I am here!

Many thanks in advance
Silvia