Fonts, PowerPoint and multiple computers do not mix. I have begun to go down the font slide: beautiful results but increasing complexity. Once you're on it, there is no way back:
  1. First level, just use one popular font, let's say Verdana (but it gets boring)
  2. Second level, group items together and "paste as PNG" back (but it is so hard to edit)
  3. Thid level, embed fonts with your PPT file
All was fine with level 3 untill I tried to use the PPT file on a Mac: disaster again. The "hardcore" solution:
For some reason, my Windows PC has far more fonts installed than my Mac. Font files are portable, they work on a PC and on a Mac. I simply copied all my PC font files and put them in a folder on my Mac desktop. If I need a font, I double click the relevant file, start PowerPoint over again and things are fixed.
Now where are these PC font files? Click "start", "run", type "%windir%\fonts" and they all show up. Select all, copy and paste them in a folder to be copied to the Mac. Done.