login php members

This is my code on the registration page (http://www.euroherp.com/register.php), that after a successful registration i get this error message
===
Warning: Cannot modify header information - headers already sent by (output started at /home/content/d/a/n/danielphillips/html/01euroherp/register.php: Cool

in /home/content/d/a/n/danielphillips/html/01euroherp/register.php on line 56
===
Where line 56 is to do with this:

===

CODE:

else
{
// Redirect to thank you page.
Header("Location: register.php?op=thanks");
}
} // end if

===

Here is the page code:

CODE:

// dbConfig.php is a file that contains your
// database connection information. This
// tutorial assumes a connection is made from
// this existing file.
include ("dbConfig.php");

//Input vaildation and the dbase code
if ( $_GET["op"] == "reg" )
{
$bInputFlag = false;
foreach ( $_POST as $field )
{
if ($field == "")
{
$bInputFlag = false;
}
else
{
$bInputFlag = true;
}
}
// If we had problems with the input, exit with error
if ($bInputFlag == false)
{
die( "Problem with your registration info. "
."Please go back and try again.");
}

// Fields are clear, add user to database
// Setup query
$q = "INSERT INTO dbUsers (username,password,email) "
."VALUES (".$_POST["username"].", "
."PASSWORD(".$_POST["password"]."), "
."".$_POST["email"].")";
// Run query
$r = mysql_query($q);

// Make sure query inserted user successfully
if ( !mysql_insert_id() )
{
die("Error: User not added to database.");
}
else
{
// Redirect to thank you page.
Header("Location: register.php?op=thanks");
}
} // end if

//The thank you page
elseif ( $_GET["op"] == "thanks" )
{
echo "
Thanks for registering!
";
}

//The web form for input ability
else
{
echo "
n";
echo "Username:
n";
echo "Password:
n";
echo "Email Address:
n";
echo "n";
echo "
n";
}
// EOF
?>

Also after verifying in mySQL the registration, and finding it successful, I go to the login page (http://www.euroherp.com/login.php)
and I already have these error messages:

===
Warning: session_start(): Cannot send session cookie - headers already sent by (output started at /home/content/d/a/n/danielphillips/html/01euroherp/login.php: Cool

in /home/content/d/a/n/danielphillips/html/01euroherp/login.php on line 9

Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at /home/content/d/a/n/danielphillips/html/01euroherp/login.php: Cool

in /home/content/d/a/n/danielphillips/html/01euroherp/login.php on line 9
===

And when I enter my correct login info, I get refused

Here is my code for the login page:

===

CODE:

session_start();
// dBase file
include "dbConfig.php";

if ($_GET["op"] == "login")
{
if (!$_POST["username"] || !$_POST["password"])
{
die("You need to provide a username and password.");
}

// Create query
$q = "SELECT * FROM dbUsers "
."WHERE username=".$_POST["username"]." "
."AND password=PASSWORD(".$_POST["password"].") "
."LIMIT 1";
// Run query
$r = mysql_query($q);

if ( $obj = @mysql_fetch_object($r) )
{
// Login good, create session variables
$_SESSION["valid_id"] = $obj->id;
$_SESSION["valid_user"] = $_POST["username"];
$_SESSION["valid_time"] = time();

// Redirect to member page
Header("Location: members.php");
}
else
{
// Login not successful
die("Sorry, could not log you in. Wrong login information.");
}
}
else
{
//If all went right the Web form appears and users can log in
echo "
";
echo "Username:
";
echo "Password:
";
echo "";
echo "
";
}
?>