Depending on the browser you are using you may get the following error when trying to access the control panel.
The site's security certificate is not trusted!
You attempted to reach XX.XX.XX.XX, but the server presented a certificate issued by an entity that is not trusted by your computer's operating system. This may mean that the server has generated its own security credentials, which browser cannot rely on for identity information, or an attacker may be trying to intercept your communications. You should not proceed, especially if you have never seen this warning before for this site.
You can just press Proceed to continue and this will allow you to login. Plesk requires you to login via SSL and since we do not install certificates for IPs this message will appear.