first off, is this what you type in browser or it's just a type? http://localhos/ localhost is correct
are you sure, you have changed the port from 8080 to 80 correctly? if yes, when you give the above address with no context path, Tomcat will display you default page from default context, the defualt context is ROOT, go to <Tomcat_Iinstalled_Directory>/webapps/ROOT to see whether this directory is exists or not, if you found no folder with name ROOT so Tomcat is right, because there is no page to display