If you are currently in a location with a strict firewall policy (e.g. a corporate environment), acccess to port 2083 may be being blocked. This will prevent access to the cPanel control panel. The same is also true of port 2087 and the WHM control panel.
You may have to ask your IT department to open up the outgoing firewall to allow you to access your control panel on ports 2083 and 2087.