I cannot access tomcat admin console?

I am try to build an app with the integration of JPA and Struts. to do it need to access tomcat manager. But when I access URL http://localhost:8080/manager/html it gives 404 Error to me.

My tomcat-users.xml

<?xml version='1.0' encoding='cp1252'?>

  <tomcat-users>

    <role rolename="manager-gui"/>
    <role rolename="manager-script"/>
    <role rolename="manager-jmx"/>
    <role rolename="manager-status"/>

    <!--<user name="admin" password="admin" roles="manager-gui,manager-script,manager-jmx,manager-status" />-->
    <user username="admin" password="admin" roles="manager-gui,manager-script,manager-jmx,manager-status"/>

    </tomcat-users>

Thanks in Advance.