Lyx Xetex and otf

[Jommelli Niccolò]

Hello
I have been trying to use XeTex with an otf font but  I cannot get Lyx/xetex
to use it. I installed the otf in the open type font directory of MikTex,
but nothing. Even if I declare the font family at the beginning of the
document, Lyx/xetex cannot find it and I get the blank pdf.
How do I get Lyx to use XeTex with otf and ttf fonts properly?
All the best