echo '<h1>Thank you for logging in</h1>';
echo '<div class="mainContent">';
echo 'Thank you, <strong class="orange">'. $username . ' </strong>you are now logged in. You are being redirected to your user panel.';
echo '<meta http-equiv="refresh" content="3;url=usercp.php">';
And the part in usercp.php
<strong>Logged In As: </strong> <span class="orange"><?php echo $_SESSION['username']; ?></span>
Why were you destroying it in the first place? What was the purpose to add it? Besides a log out system..
"The reasonable man adapts himself to the conditions that surround him... The unreasonable man adapts surrounding conditions to himself... All progress depends on the unreasonable man." - George Bernard Shaw