How to Enable a Java Runtime Environmentby Chris Hoffman
Oracle's Java runtime environment software runs applications written in the Java programming language. After installing the free Java runtime environment on your computer, it's always available for desktop applications. But, since Java also runs Java applications embedded on Web pages, the Java runtime environment plug-in for Web browsers can be disabled or enabled separately. You can enable the Java runtime environment through your Web browser's configuration window or the Java control panel.
Click "Start" and "Control Panel."
Double click the coffee-cup-shaped "Java" icon in the "Control Panel" window on Windows XP. On newer versions of Windows, click "Programs" in the "Control Panel" window and click the "Java" icon.
Click the "Advanced" tab at the top of the Java "Control Panel" window.
Click the plus sign to the left of "Default Java for Browsers" in the list of advanced settings.
Check the boxes to the left of "Microsoft Internet Explorer," "Mozilla Family" and "Netscape" by clicking them.
Restart any running Web browsers by closing all of their windows and re-opening them.
Click "Tools" and "Internet Options" in the Internet Explorer window.
Click the "Advanced" tab at the top of the "Internet Options" window.
Scroll down to "Java" in the list of settings on the "Advanced" tab and click the box to the left of the installed Java version if it isn't checked.
Click the "Security" tab.
Click the "Custom Level" button.
Scroll down to "Scripting of Java Applets" in the list and click "Enabled" under it.
Click "OK" twice.
Click "Tools" and "Add-ons" in the Mozilla Firefox window.
Click the "Plug-ins" icon at the top of the Add-ons window.
Click "Java" in the list of installed plug-ins.
Click the "Enable" button if Java is grayed-out and disabled.