None of my graphs are showing - they are just an "x" ??
It's most likely a problem with the java installation on your computer. Try the information in these links and let me know if it works:
http://www.java.com/en/download/manual.jsp
http://www.beginnertriathlete.com/cms/article-detail.asp?articleid=673
I had the same problem some time ago. Just needed to update to the latest JAVA add on.... Like marma said....