JQuery issue -what is wrong with my code?

[Confidence]

hi

 

i have cascading select lists (1 select list gets generated based on choice of higher one...like country-> city)

 

and i want user interaction blocked until i get the data from database

i use jquery with blockUI...and it is added in header too....but it is not working....it does not block page when i chose something....what is wrong with my code?

   1.
              $('#provider').change(function() {
   2.
                      $.blockUI();
   3.
              $('#tarif').load("ajax/order.php?atask=gettarifs", {
   4.
                              'selectprovider' : $('#providerselect').val(),
   5.
                              'kwhforajax' : $('#kwhforajax').val(),
   6.
                              'current' : $('#current').val(),
   7.
                              'zip' : $('#zip').val()
   8.
                      });
   9.
              $.unblockUI();
  10.
              });