<?
//mysql connections
$username='Admin'; //from mysql in your script

$username=strtolower($username);
if (isset($_POST['username']))
    {
    $_POST['username']=strtolower($_POST['username']);
    if ($_POST['username']==$username)
        {
        //login
        }
    }
?>
<form method='post'>
<input type='text' value='adMiN' name='username'>
<input type='submit' value='submit'>
</form>

<?
//mysql connections
$username='Admin'; //from mysql in your script
 
if (isset($_POST['username']) && $_POST['username']==$username)
    {
    //login
    echo "test";
    }
?>
<form method='post'>
<input type='text' value='adMiN' name='username'>
<input type='submit' value='submit'>
</form>

session_start();
//mysql connect code
 
$result=mysql_query("SELECT * FROM `users` WHERE `username`='".$_POST['username']."' AND `password`='".$_POST['password']."'");
 
if (isset($_POST['username']) && mysql_num_rows($result)==1)
    {
    $row=mysql_fetch_array($result);
    $_SESSION['username111']==$row['username'];
    unset($row);
    header('Location: index.php?login=true');
    //there should be no browser output before this line.
    }
?>
<form method='post'>
<input type='text' value='Admin' name='username'><br>
<input type='text' value='password' name='password'>
<input type='submit' value='submit'>
</form>

<?
session_start();
if ($_GET['login']=='true' && !isset($_SESSION['username111']))
    {
    echo "<h1>You need to be logged in to view this page!</h1>";
    exit;
    }
//no browser output before this line.

when you use md5 you got this value in database
admin= 21232f297a57a5a743894a0e4a801fc3

ADMIN= 73acd9a5972130b75066c82595a1fae3 

AdMiN= 2714cba6c6d58e587565cf4e6b275078 

$con = mysql_connect("localhost","root","");
	if (!$con)
	  {
	  die('Could not connect: ' . mysql_error());
	  }
	  else
	  {
	 // echo('Connected with Mysql');
	  }
		@mysql_select_db("db_login", $con);
		if (isset($_POST['Submit']))
		{
			$user_uname=$_POST["user_uname"];
			$user_pass=md5($_POST["user_pass"]);
											
			
			$sql=mysql_query("SELECT * FROM table WHERE user_uname='$user_uname' AND user_pass='$user_pass'");
			
			if (mysql_num_rows($sql)==0 || mysql_num_rows($sql)>1)
			{	
				echo "<script>alert('Username/password pair is invalid.Please try again.')</script>";
				
				echo"<script language='javascript'>window.location.href='login.php'</script>";
			}
			while($row = mysql_fetch_array($sql))
				  {
					if($user_pass==$row['user_pass'] and $user_uname==$row['user_uname'])
					{
						//here use go to your new page						echo"<script language='javascript'>window.location.href='newprofile.php'</script>";
						}
						else
						{
													echo"<script language='javascript'>window.location.href='login.php'</script>";
						}
					}
				  }
				  echo"<script language='javascript'>window.location.href='login.php'</script>";
		} 
}