Are you using a different skin? If so, try changing back to the default & see how it goes.

Also make sure your Java's up to date. Use the JRE offline installer here & remove your current Java version before you install the new one.
http://java.sun.com/javase/downloads/index_jdk5.jsp

Otherwise, I wouldn't have a clue. Use the forum search to look for font...see if you can find any old threads to help