How to find out what's going wrong ?? (can i post my simple servlet program.)
As I tried to point out, your program has NOTHING to do with your problem - Tomcat is not even trying to load your program so any program errors remain undiscoverable.
It is your configuration - ie the directory organization/layout and configuration files - which Tomcat is not recognizing as a web application.
Presumably your tomcat installation has some working applications such as "examples." Study how working examples are laid out.
One common beginner error has to do with directory names -
Java cares about case in directory and file names even if windows doesn't.
So web-inf will not be recognized - WEB-INF is required, etc etc.
Bill