I can not run Apache Tomcat for servlets!

[xploreraj]

I can not run Apache Tomcat for servlets. Normal Java programs are running.

I have installed the JDK (jdk1.6.0_18 & jre6) & Tomcat 5.5 properly.
The port no. for Tomcat is 8080. I don't think any other application is using that port.
I did the following:

->removed "invoker" comments in installdir\conf\web.xml.
->put my .class files in instaldir\webapps\ROOT\WEB-INF\classes.
->modified environment variables for JAVA_HOME (set to JDK directory), CATALINA_HOME (set to Tomcat5.5 directory), and CLASSPATH (set to installdir\common\lib\servlet-api.jar).
->restarted the server.

The problem is that not even the home page is opening through http://localhost:8080 in IE and Opera 10.6. In Firefox, although the index page is opening, but the http://localhost:8080/examples/Servlets (for Servlet Examples) and other pages are even not opening.

Even if sometimes it opens, it might work or not. But after some time, the problem reoccurs and persists.

ERROR: Page not found (404).

Configuration:
S/W: Firefoz 3.6, Opera 10.6, JDK 1.6.0_18, Tomcat 5.5.
H/W: Windows XP SP2, Intel Core2Duo T6600, 3GB RAM, 320 GB HDD.

Infinite times I installed and uninstalled Tomcat.
Please solve my problem.
Thanks a lot