A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
As a test, try changing the text to one of the fonts supplied with Windows or Office (Arial, Calibri are good choices). If the text now appears in presentation mode, the problem is likely due to a recent update from Microsoft.
Removing the update will fix the problem.
Troy Chollar's blog post explains more about the problem and shows you how to fix it:
http://thepowerpointblog.com/2012/12/13/ms-security-update-makes-fonts-not-seen