jquery - Tablesorter, PHP and AJAX -

i have problem when try sort table tablesorter.js. looks easy use it, in case doesn't work... first of all, explain application:
1.- have database several data
2.- developed web interface search data (html)
3.- wanted make interactive communication database, used ajax
4.- build querys , table results in php file

so, in html file:

<div id = "divresults"></div> 

and in header of file added jquery , tablesorter.js references , css file contento of css tablesorter

$(document).ready(function()     {         $("#mytable").tablesorter();     } );  

now, in php file have following code:

    <table id="mytable" class="tablesorter" style="font-size: 8pt; position:relative; top: -10px;" >                     <thead>                         <tr>                             <th><b>col1</b></th>                             <th><b>col2</b></th>                             <th><b>col3</b></th>                             <th><b>col4</b></th>                             <th><b>col5</b></th>                         </tr>                     </thead>                     <tbody>      <?php          ($i = 0; $i<$n;$i++)            {                $result_array = ordenar_array($result_array,2, sort_asc,3,sort_asc);               echo "<tr>";               ($aux = 0; $aux<5;$aux++)             {                echo "<td> ".$result_array [$i][$aux]."</td>";             }              echo "</tr>";           }     echo "</tbody>";     echo "</table>";     ?> 

the table it's ok, data ok , display in correct way, can't sort function. me?

edit: code added css file:

/* tables */ table.tablesorter {     font-family:arial;     background-color: #cdcdcd;     margin:10px 0pt 15px;     font-size: 8pt;     width: 100%;     text-align: left; }  table.tablesorter thead tr th, table.tablesorter tfoot tr th {     background-color: #e6eeee;     border: 1px solid #fff;     font-size: 8pt;     padding: 4px; } table.tablesorter thead tr .header {     background-image: url(../img/bg.gif);     background-repeat: no-repeat;     background-position: center right;     cursor: pointer; } table.tablesorter tbody td {     color: #3d3d3d;     padding: 4px;     background-color: #fff;     vertical-align: top; } table.tablesorter tbody tr.odd td {     background-color:#f0f0f6; } table.tablesorter thead tr .headersortup {     background-image: url(../img/asc.gif); } table.tablesorter thead tr .headersortdown {     background-image: url(../img/desc.gif); } table.tablesorter thead tr .headersortdown, table.tablesorter thead tr .headersortup { background-color: #8dbdd8; }