The Plesk surface normally can be reached via the following SSL encrypted URL:

https://xxx.xxx.xxx.xxx:8443

The "x" characters have to be replaced by your own server IP address. Alternatively the official server name can be used instead of the IP address.

You will find the login data in the particular server data of the concerned server at the point "Default-Password for SSH or Webpanel (admin/root/Administrator)".