$.post not working correctly

$.post not working correctly

Hi Everyone,
                  I'm a newbie in the usage of ajax request using jquery.I have used it for my administrator login form and it is working correctly.In the home page to which it is redirected, I'm using jquery with ajax for 'logout' and for adding data through form.The 'logout' functionality is working correctly but the form submission is not.I have checked the path of the php file to which data is sent for manipulation, and it is correct.Whenever I submitted the form, the page somehow gets refreshed and no output is displayed.The 'news.php' file is in the same folder as the page in which jquery is executed.
 
                 I've tried 'alert' ing the data before the '$.post' function and it is displaying correctly.Here is the code that I'm working in:

//html file:

                $(document).ready(function(){
                 $("#logoutbtn").click(function(){
                  $.post("login.php",{logout:1},function(data){
                   if(data.success){
                     location.href=data.redirect;
                   }
                  },'json');
                 });
                 $("form#addNews").submit(function(){
                  $("#errdiv").hide();
                   alert("Here")
                   $.post("news.php",{ftitle:$("#title").val(),fdesc:$("#desc").val()},function (data){
                    if(data.success){
                     $("#errdiv").html(data.message).fadeIn();
                    }
                    else{
                      $("#errdiv").html(data.message).fadeIn();
                    }
                   },'json');
                });
              });

//php file:

    if($_POST){
       $data=array();
       $ftitle=$_POST["ftitle"];
       $fdesc=$_POST["fdesc"];
       //Insert query
      if(successful insert)
        $data['message']="Data inserted!!";
      }
      else{
        $data["message"]="Insertion Error!!"
      }
   echo json_encode($data);
}