pages numbers didn't effect in php paging

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PHP

hi all
i have php page that i want to apply paging on it , but there is a problem, when i choose page no 2 for example , it has no sense and there is no effect in displaying new data. plus to this that i have two drop down list , when i change the page no , the selected items of these list go the default form not to the selected i have made.
here you are my code , any help please as i don't know php well

if(isset ($_GET['kat']))
          {
          $subkat=$_GET['kat'];
          $mainkat=$_GET['mainkat'];
          $qmainkat="where maincategory='$mainkat'"; 
          $qkat=$qmainkat." and category='$subkat'";
          echo "<br>[<a href='adm_shop_add.php'>">ADD NEW</a>]";
          
          
          
          $qsh="select * from shop_item $qkat order by postdate desc ";
          $rs_sh=@mysql_query($qsh);
          $ada_sh=@mysql_num_rows($rs_sh);
          if ($ada_sh>0){ 
          if(isset($_GET['page']))
          {
           $pageNum = $_GET['page'];
          }
          else
          {
          $pageNum = 1;
          }
          $offset = ($pageNum - 1) * $rowsPerPage;
          $result=@mysql_num_rows(@mysql_query("select id from shop_item $qkat"));
       
          $query   = "SELECT COUNT(id) AS numrows from shop_item $qkat ";                      
          $result  = mysql_query($query) or die('Error, query failed');
          $row     = mysql_fetch_array($result, MYSQL_ASSOC);
          
          
          $numrows = $row['numrows'];
          
          
          $maxPage = ceil($numrows/$rowsPerPage);
            
          
          $self = $_SERVER['PHP_SELF'];
          $nav  = '';
          for($page = 1; $page <= $maxPage; $page++)
          {
            if ($page == $pageNum)
            {
            $nav .= " $page "; // no need to create a link to current page
            }
            else
            {
             $nav .= " <a href=\"$self?page=$page\">$page</a> ";
            }
         }
         // print the navigation link
         echo $first . $prev . $nav . $next . $last;        
          
          echo "<table border=0 cellpadding=8 cellspacing=8 >";
          echo "<tr>";
          while ($ro_sh=@mysql_fetch_array($rs_sh))
          {
          $row++;
          echo "<td valign=top align=center >";
         if (!empty($ro_sh[picture]))
         {
            echo "<img src='".$ro_sh[picture]."' border=0 width=120>";
         }         
         echo "</td>";
         echo "<td valign=top >";
         $kategoriname=@mysql_result(@mysql_query("select name from shop_kat where id='$ro_sh[category]'"),0,0);
         echo "".$ro_sh[title]."";
         echo "<br><small>".$ro_sh[description];    
         
         echo "</td>";
          echo "</tr>";
          echo "<tr>";
          }
          echo "</tr>";        
          echo "</table>";
          
          }
          }

thanks