How do I install a new font?

I work in Sibelius to create musical scores and now the publisher I am working for wants the Zapf Chancery fonts as title for their Christmas Collection but I can't get this fonts available in Sibelius. I installed it by dragging the fonts in the user fonts folder and the system fonts folder. I also used fonts-book (set to computer in preferences) and installed it there, it was accepted as valid and restarted the computer. Still the fonts doesn't appear in Sibelius or any other kind of program. How can I get it correctly installed? The font format is otf, I also tried the ttf format.Nothing helps. Any suggestions?