3
It could be permitions not set for that block. To set them go to Administration Menu -> System Admin -> Groups, Select the Group you want to edit from "Edit groups" table, make the changes and click "Update Group"
It also could be a problem with block. Try to enable PHP debug mode in Administration Menu -> System Admin -> Preferences -> General settings and for "Debug mode" select PHP Debug, scroll down and click go. Look for errors, just ignore all notices.
You may try to clean cache - delete all files except index.html in template_c folder.