Question mark on special chars

Yesterday i was working on a file when notepad++ crashed. I then went in the backup folder of the program to restore the file. After the restoration, special chars (such as € or accented letters) are displayed as a question mark in a black diamod. What is strange is that this happen only in this page, the other pages in the whole WP are displayed correctly! I trashed the file and wrote a new file with the same name and the same shortcode but the problem persist! How can i fix this?