check your classpath and make sure you're leaving the ".class" off of the file when you run it. so, if your file is Hello.class, you'd do:
oh, and you can try this to see if your classpath is screwed up...
again, assuming your java class file is called Hello.class, run this:
that's basically saying "including the current directory in my classpath when trying to run this"
if that works, then the problem is with your classpath.
oh, and any java class you run directly must have a method with the following signature:
Code:
public static void main(String[] args) { <your code here>}
if you don't have a method that looks like that, you may want to reread chapter one of your tutorial