Your Mathematica is not finding the Mathematica fonts.
Sounds like you did the first test, but I include it for completeness.
The Mathematica preference and cache files can be reset by holding
down the SHIFT and OPTION keys as Mathematica starts. If that does
not correct it, the bigger hammer is to delete the folder
under your home directory. It might be necessary to do this again after a system restart.
If that does not correct the problem, open the FontBook application (/Applications or /Applications/Utilities),
select all fonts, and use File menu - Verify Fonts to check for
damaged or corrupted fonts. If a font is marked as a problem font,
please either disable it or re-install that font from the operating
system CD. If there are duplicate fonts, disable all but one copy.
If the FontBook application has a
File menu - Restore Standard Fonts
item, that will be quicker. Third-party fonts that were added later
will need to be installed again.
Next would be to delete the current Mathematica 9,
re-download it, and re-install.
Sorry about the difficulty.