MikTeX fails to find a font installed in Windows 10 (for XeLaTeX)

[P P Narayanaswami]

Thanks for your suggestion.
Just using "Gayathri" (instead of Gayathri Regular) for the fontname 
works.
And, to get a bold version (Gayathri Bold), I used \textbf...}, and it 
works.
But the font has a thin version Gayathrti-thin.  There is
no LaTeX/XeTeX font changing command for to typeset the "thin" version" 
of the same font.