thank you Roedy.. let's see..

1. not this one, since am not running in browser (compiling/running
stand-alone's in command-line..)

2.  'class mentioned' is class you're trying to run right? for testing
purposes am trying to run a hello.java, very simple, thus:

import java.io.*;
class hello {
  public static void main(String args[]) {
    System.out.println("hello");
  }
}

compiles (javac hello.java) but won't run (java hello)
   NONE of the other .java's I have in my HD is now running (in all
cases, compiled again, b/c just re-installed JVM, but they won't run...)

again, as have been advised many times here do not have a classpath set,
this has always worked for me (but how? it says here
http://java.sun.com/j2se/1.3/docs/tooldocs/win32/classpath.html

that if you don't set classpath java looks for it in same directory of
class you're trying to run ("current directory"..) I have always been
able to compile/run classes from anywhere in my HD w/o having set
classpath..  ?????

I have been running JVM on my machine (W2000) for over a year now, all
of a sudden my classes won't run.. this is truly bizarre...

3. can't do diagnostic, as can't run any code....;)

4. nothing serialized involved.

5. don't have classpath set (except for Tomcat, thus:
      CLASSPATH=c:\tomcat\common\lib\servlet-api.jar)

just tried running this:

   java hello -classpath c:\j2sdk1.2_11\jre\lib\rt.jar

but got exact same error: Exception in thread "main"
java.lang.NoClassDefFoundError: hello

I really don't get this...  (rt.jar is where system API is, right? also,
I doubt it's a classpath problem b/c can compile fine..)

it seems JVM can't find the class I'm trying to run, but it's there, I
can see it...  WEIRD.....

thank you Roedy....    :(