after update wordpress from 2.0.4 to 3.3.1 the site displays greek characters like question marks ????? in the old posts (content and title), as you can see at http://www.elliniko-fenomeno.gr . The strange think is that in the database, the greek characters displayed correctly, when i change the charset of DB and wp_post table from greek_general_ci to utf8 and collation to utf8_general_ci. In the wp-config.php there is no define('DB_CHARSET', 'utf8') and define('DB_COLLATE', ''). When i try to add them, the old post fixed, the new turn ???? but the worse is that i can't access to wp-admin(you do not have sufficient permissions to access this page).
Any help please?