Maybe some more details will help:
-Is it only one font that's behavintg this way? Which one? What kind of font is it (TrueType, PostScript, etc... ) What is it's "kind" on the desktop, in a window or in Get Info>?
-What version of Photoshop are you using? Do you have other Adobe applications, and does the font show up in them?
-Font Book is showing the font in three locations. Not that this should prevent it from showing up in Pshop's menu, but: do all three locations have the same version of the font? (Select each one in the Font Book Font list, and set Preview menu to Font Info to get that info)
-How did the font get where it is? Did you install it through Font Book? Did you drag it into the various Fonts folders? Going through Font Book validates the font - checks the file for corruption; a direct drag doesn't validate. But once they're in Font Book, you can use the Validate Font command to check the files, so select each of the three versions in turn and do the Validate.
If it makes you feel any better, there's no obvious reason the font isn't showing up. And, of course, people shouldn't have to be techies to make this stuff work right!