If the calculators do not start this is sometimes due to the fact that the browser’s Java extension (Java plug-in) is not activated. Please check the following settings first.

Internet Explorer: Tools - Manage add-ons - Java ... - Enable
Firefox: Add-ons - Plugins - Java ... - Enable

Mac OS:
Safari: Preferences - Security - Enable Java
Firefox: Tools - Add-ons - Plugins - Java ... - Enable

Often there is no Java plug-in at all. Downloading the current version is relatively easy and will certainly pay off!