This post may be of use to people experiencing the same problem I had. When I opened PowerPoint slides sent by a coworker, I was getting blank slides. Attempting to switch to outline view would crash PowerPoint. A search for possible solutions yielded inconclusive posts or dead-ends.
After much twiddling, it turns out the problem was with a misconfigured Arial font. Microsoft in its great wisdom installs a copy of Arial that conflicts with the system-supplied one, as explained in Karl Lang’s must-read article on OS X font management, but that was not the root cause of the problem.
Arial was not appearing at all in the PowerPoint font menu, and opening the slides in Keynote yielded a font warning saying non-existent Arial was replaced by Arial Narrow. Clearly PowerPoint is much less resilient than Keynote to missing fonts (crashing in outline view mode is inexcusable, but that’s Microsoft coding sloppiness for you). If Arial is so vital, it should have been included as a resource in the application bundle itself, but I digress.
Font Book did show Arial as installed, with only a single copy after I purged the conflicting fonts as per Kurt Lang’s recommendations. Validating Arial in Font Book yielded a warning about duplicate fonts, but with no indication of where the duplicate may be, since Font Book itself did not know of any other instance.
It turns out I had an old pre-OpenType copy of Arial in my ~/Library/Fonts folder that was causing a conflict. It was functional enough to be picked up as conflicting and disabling Arial in PowerPoint and Keynote, but not functional enough to be listed by Font Book. I am not sure how it got there, possibly from an older version of Office and transferred over many machine upgrades. Removing the file fixed the problem. of blank slides and the crash in switching to outline view.
Of course, if you care at all about typography, you should use Helvetica rather than an inferior ersatz like Arial, but Arial is so prevalent in the taste-impaired Windows world that one cannot escape its gaucheness entirely.