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