InDesign should see any fonts that are installed normally on your sytem for use by all programs (you don't mention your OS, so I don't know how you would normally install fonts). There are also two special private folders, one for all Adobe apps, and one for InDesign alone, and copying a font into either of those folders should also work. Is this perhaps a Type 1 font and you only have half of it? Or perhaps you are trying to install a Mac font on Windows? That would be apparent if the font size in Explorer is listed as 0 bytes.