So you have a problem with the classpath when you try to run classes from the classpath. Eclipse would be irrelevant to that problem because it has an entirely different way of setting the classpath (which it calls "build path").
You will need to provide the source for class A because a simple "hello world" app works with the steps you posted. In particular, does A extend anything, or does A require other classes? The source would answer these questions.
And by the way, please pay attention to the private message sent to you. Fixing your display name is not an option!