$(function(){

    //code below will be executed when the submit button being clicked
    $('form.appnitro').submit(function() {

      if($("#element_1").val() != "xyz"){

        alert("Incorrect text entered!");

        //restore the submit button
        $("#li_buttons > input[type=submit],#li_buttons > input[type=image]").prop("disabled",false);

        //cancel the form submission
        return false;
      }
    });
});