If the content editor of SHFB opens without any functionality then the configuration file is corrupt.
This is repairable through deleting the config-files under C:\Documents and Settings\[YOUR_USER_ID]\Local Settings\Application Data\Eric_Woodruff\...
Sometimes an error occured during opening content editor next time. In this case you must study the message. Offen you have created a not XML-wellformed content file. Open your last used files with an other XML-editor and look for the place which is described in the message.
After fixing the prob you must close SHFB, delete the config-file again and reopen your SHFB-project.