You may experience issues with the non-standard http ports Cpanel works with. Usually Cpanel can be opened from:
Sometimes local firewalls allow only access to sites on port 80. In such cases, use the last URL. Note that the address "3" is a web based proxy which provides you with the option to access your cPanel via the default http port 80. We have set this extra service for our Customers which Internet Service Providers blocked ports 2082 and 2083.
You may check if the ports are blocked executing the following commands: