In order to greatly increase the security of your WordPress installation, secret keys must be set up. This should be part of the standard installation process. Whenever there is suspicion secret keys have been compromised, the administrator must change them. Changing keys will invalidate all sessions and users will need to re-authenticate.
Here is how you can set up secret keys:
Step 1 – Get unique secret keys and copy them from WordPress secret key generator- https://api.wordpress.org/secret-key/1.1/salt/
Step 2 – Access your site with an FTP client, and go to the public_html directory.
Step 3 – Open wp-config.php file and paste the keys there.
Step 4 – Save it and upload back to the server.
See if your website is running fine.