Your screenshot http://www.hostingpics.net/viewer.php?id=138868Capturedcran20150806233459.png shows that it’s a localhost installation. It’s different from http://wp.melodix.fr/ which is online.
Did you do any custom css on your localhost installation? You can install firebug and check the error console for any clue. It could also be a third party plugin conflict.
We can only verify that http://wp.melodix.fr/ works properly on our browsers, we cannot troubleshoot the issue on your localhost.