You do not need to "import" fonts into FrameMaker. FrameMaker can access the fonts in the windows fonts folder.
Did you restart FrameMaker after installing the fonts?
Do the fonts show up in other windows software like Microsoft Word?
Which type of font is it (e.g. TrueType, OpenType, Type1)?. Are the fonts in some way "special"? Are they standard fonts from a font library or a special font (self-created)?
Also, you might want to check the font name. The font name specified in the font might be a completely different one than the font file name. Also, some fonts show up "somewhere else" in the font menu. Like let's say Helvetica Neue might appear not under H but maybe under L like "Linotype Helvetica Neue" (or whatever, just as an example).
By the way, any kind of additional information like Windows version and FrameMaker version might be helpful as well.
Thank you very much for your information.