Thank you both for the answers.
Since you said about ftp I downloaded filezilla and did some experiments. I don't know much about FTP so I tried the "quick connect" option which only asks "host", "username" and "password".
I put my domain name as a host (not my hosting service.. right?)
My ftp username (my hosting provider adds automatically a new ftp user)
And my password. I connected successfully but the only things I can see there are only 2 directories. The "Maildir" and "logs". "Logs" have nothing inside. A Wp folder doesn't exist. Now? Whee can I find wordpress?
PS: Yes he did say something similar. To be exact: First, open the file wp_config.php and find the text "define ('WP_DEBUG', false);" and replace "false" to "true". What you said and what he said is the same thing?