Databse conection error in admin panel plugin

Databse conection error in admin panel plugin

hi i have problem in my admin panel wordpress all website is done and work

only i have problem in my plugin in admin panel when clik plug in show “Database conection error”

plugin show corectlly in my website only not show in admin panel …

and when i create test.db file in public_html show me http error 500
test db.php file code :

<?php
$link = mysql_connect(‘your_hostname’, ‘database_username’, ‘database_password’);
if (!$link) {
die(‘Could not connect: ‘ . mysql_error());
}
echo ‘Connected successfully’;
mysql_close($link);
?>

please help