This section describes you some of the trouble shooting when your applet is not working in the browser
Are you running Mac OS 9?
Firstly check which browser are you using. If you are using Netscape 4.0(or less) with MacOS then try to run the applet applet on Internet Explorer or on different Operating system like Linux.
What version browser do you have?
Check the version of your browser by clicking on the ?Help? menu and then select the ?About?. And make you using at least version 5.0 (Netscape / IE).
Is your browser set to run Java?
If above things are ok then may be your browser does not configure to run java.
Does your browser support java 1.3?
Now Internet Explorer 6.0 on Windows XP is also comes without Java support or with the old Java support like Java 1.1. To fix this problem you have to install the browser plugin from the Sun's website.
Recommend the tutorial