Open the Find Fonts dialog in InDesign and look at the missing font. To the right of the font you'll see an icon of either an "a" "TT" or "O" which indicates Postscript, TrueType, or OpenType respectively. If the missing font indicates anything other than an "O", that means that the original file utilized a different format than the one you are activating and InDesign still will not recognize it. You can always replace the font with the OpenType equivalent if InDesign sees it. Alternatively, a good way to force InDesign to load the font, is to place the OpenType font in a folder called Document Fonts that resides in the same folder as your InDesign file. If you close your file and re-open, InDesign will automatically load the fonts in the Document Fonts folder.
I think the documents fonts folder in on a Mac. Do you know where I should load these fonts in a PC with Windows 7?
Document Fonts (case sensitive) folders can be used on both platforms. Any fonts included in such a folder in the same parent folder as a .indd file opened in CS5 or later will be used instead of fonts installed on the computer, presuming the fonts are either Windows TT or OpenType fonts, or in the case of Mac TT or .dfont, are being opened on a Mac (these formats will not be used on Windows no matter how you try to install them). My recollection is that T1 fonts are not usable with the Document Installed Fonts feature.