Multiple Issues When Logging Into WP Admin

I am having multiple issues while trying to log into the admin panel of my website. I get a blank screen after entering my password; enabling Debug mode via wp-config.php shows the following errors:

Deprecated: mysql_connect(): The mysql extension is deprecated and will be removed in the future: use mysqli or PDO instead in /home/http/chris.urquhart/curquhart.co.uk/http_site/wp-includes/wp-db.php on line 1562

Notice: wp_enqueue_script was called incorrectly. Scripts and styles should not be registered or enqueued until the wp_enqueue_scripts, admin_enqueue_scripts, or login_enqueue_scripts hooks. Please see Debugging in WordPress for more information. (This message was added in version 3.3.0.) in /home/http/chris.urquhart/curquhart.co.uk/http_site/wp-includes/functions.php on line 4148

Warning: Cannot modify header information – headers already sent by (output started at /home/http/chris.urquhart/curquhart.co.uk/http_site/wp-includes/wp-db.php:1562) in /home/http/chris.urquhart/curquhart.co.uk/http_site/wp-admin/includes/misc.php on line 1116

I got in touch with my uncle (who hosts the site) and he said the first issue had been fixed; I assume this means he changed it from MySQL to something else, but I still get the white screen of death.

Line 1562 of wb-db.php looks like this:

$this->dbh = mysql_connect( $this->dbhost, $this->dbuser, $this->dbpassword, $new_link, $client_flags );

Line 4148 of functions.php looks like this:

trigger_error( sprintf( __( '%1$s was called <strong>incorrectly</strong>. %2$s %3$s' ), $function, $message, $version ) );

And line 1116 of misc.php looks like this:

header( sprintf( 'Referrer-Policy: %s', $policy ) );

I’m not an expert in PHP, so I can’t understand why these things are causing me such a headache; any and all help in fixing these issues is greatly appreciated.

If I’ve missed out any information, please let me know and I’ll provide it ASAP.

The page I need help with: [log in to see the link]