java.lang.NoClassDefFoundError

I have newly installed Java 1.3.1 and Textpad 4. I am trying to run the following program:
public class Hello
{ public static void main(String args[])
{ System.out.println(“Hello, World!”);
}
}
It works on other computers, but not on my home computer. It compiles fine, but when I run it, I get the following error:
Exception in thread “main” java.lang.NoClassDefFoundError: Hello
This same error comes up for every program I try to run.
I am getting suggestions to change the classpath in DOS, but that does not work, and I shouldn’t have to do this for every program I run…any suggestions?