UTF problem

I have seen similar problems in the forum, but they have been solved by disabling some plugins – but I have fresh WP installation without any plugins used. The problem is still there. Everything is set up in UTF-8 (I never use anything else), but some characters are shown (in posts, comments, in admin interface, in the final page – everywhere), as a strange black character (it seems to be a 3-byte character, shows like 3 characters when the browser is set to ascii) and a question mark. The problematic character is for example uppercase norwegian slashed O (Ø), the same character in lowercase is ok. There are other problematic characters too. The site is http://ao.kyknos.org/kyklog/