Activation Help (PHP)

PHP Code:

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<?php
include("global.php");

if($_GET['action'] == "activate"){
    $key = $_POST['key'];
    $kr = mysql_query("SELECT activationkey FROM users");
    $keyrow = mysql_fetch_array($kr);
    $nr = mysql_query("SELECT fname FROM users WHERE activationkey = '$key'");
    
    if($keyrow = $key){
        $update = mysql_query("UPDATE users SET activated = yes WHERE activationkey = '$key'");
        echo "Congratulations '$nr' - your account is now activated.";
    } else {
        echo "This account has already been activated.";
    }
} else {?>

<form action="?action=activate" method="POST">
<input type="text" name="key"></input>
<input type="submit" value="activate">
</form>

<?php
}
?>

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The user receives their key in an email btw. My problem is that when I put in the key it doesn't match it to a user thus not updating the 'activated' field nor displaying their name in the echo.