Problem in update

Hi., I want to update an entry that ive selected from a table.
Everything is running but the data does not update>

This is the code of the Table where I select the data.

<?php 

$conn=mysql_connect("localhost","root","");
	if(!$conn)
	{
	die('could not connect!' . mysql_error());
	}

	mysql_select_db("people", $conn);
$result = mysql_query("SELECT * FROM usersinfo"); ?>

<table>
  <tr>
    <td>Recent Posts</td>
  </tr>
  <?php while($row = mysql_fetch_array($result)) : ?>
  <tr>
    <td><?php echo $row['USERNAME']; ?></td>
    <td><?php echo $row['LASTNAME']; ?></td>
	    <td><?php echo $row['FIRSTNAME']; ?></td>
    <td><?php echo $row['MI']; ?></td>
	    <td><?php echo $row['COMPANY']; ?></td>
    <td><?php echo $row['POSITION']; ?></td>
	  <td><?php echo $row['DEPARTMENT']; ?></td>
    &lt!-- and so on -->
    <td>
      <form action="delete.php" method="post">
        <input type="hidden" name="delete_id" value="<?php echo $row['ID']; ?>" />
        <input type="submit" value="Delete" />
      </form>
	  <form action="modifypage.php" method="post">
		<input type="hidden" name="modify_id" value="<?php echo $row['ID']; ?>" />
        <input type="submit" value="Modify" />
      </form>
    </td>
  </tr>
  <?php endwhile; ?>
</table>

This is the code for the page where I input the new data

<?php
 echo"<form name='myForm' action='modify.php' method='post'>";
 echo"<br>";
 echo "Lastname: <input type='text' name='ace_firstname'>";
  echo"<br>";
 echo "Firstname: <input type='text' name='ace_lastname'>";
  echo"<br>";
 echo "Midlename: <input type='text' name='ace_middlename'>";
  echo"<br>";
 echo "Company: <input type='text' name='ace_project'>";
  echo"<br>";
 echo "Position: <input type='text' name='ace_department'>";
  echo"<br>";
 echo "Department: <input type='text' name='ace_position'>";
  echo"<br>";
   echo "id: <input type='hidden' name='ace_id' value='" . $modify . "'>";
  echo"<br>";
 echo "<input type='submit' value='Submit'>";
 
 

?>

and this is where the update happens

<?php

$MODfirstname=$_POST["ace_firstname"];
$MODlastname=$_POST["ace_lastname"];
$MODmiddlename=$_POST["ace_middlename"];
$MODproject=$_POST["ace_project"];
$MODdepartment=$_POST["ace_department"];
$MODposition=$_POST["ace_position"];
$MODid = ($_POST['ace_id']);

$con = mysql_connect("localhost","root","");
if (!$con)
  {
  die('Could not connect: ' . mysql_error());
  }

mysql_select_db("people", $con);

mysql_query("UPDATE usersinfo SET LASTNAME='" . $MODlastname . "', FIRSTNAME='" . $MODfirstname . "', MIDDLENAME='" . $MODmiddlename . "', PROJECT='" . $MODproject . "', DEPARTMENT='" . $MODdepartment . "', POSITION='" . $MODposition . "' WHERE ID=' " . $MODid . " '");

mysql_close($con);
?>

Can anyone review my code especially on the update query Ive probably missed out something . Thanks in advance.