Do not forget to change 127.0.0.1 with the IP of your server.
Also if you have a domain correctly pointed to your server's IP address it can be used like
https://www.onlinehowto.net:8443
Then if everything is fine you will see the Plesk login screen waiting for username and password as it is shown on the next picture above this paragraph.
Important: If you have more than three failed attempts, the login will be locked out for 30 minutes! In this case you can unlock it using one of these tutorials according to your operating system on the server:
Unlocking Plesk control panel under Linux