Plesk comes with a trial license key, which is automatically installed to the control panel. This license key allows you to create one user account, host one Web site and one mail box. Therefore, to fully use the Plesk Control Panel as you need, you should obtain a license key from Parallels or one of its resellers and install it to the control panel.
Plesk license keys have a built-in expiration date. This has been implemented to help prevent fraud and theft. It requires the Plesk software to check with Parallels licensing server during a 10 day grace period (prior to the expiration date) to verify that the key has not been reported stolen and is being used in accordance with the End User License Agreement (that is, installed on only one server). Once this is verified, the expiration date is prolonged.
Plesk will attempt to connect over TCP/IP to the licensing server through port 5224. Please make sure that this is not blocked by a firewall. The update process runs automatically and the Plesk administrator does not need to do anything unless there is a problem. Should the Plesk key expire, check your firewall and then go to Server > License Management and click Retrieve Keys. If the key cannot be updated, contact your reseller or Parallels (if you purchased the license key directly from Parallels).
You can test the connection to the licensing server anytime by going to Server > License Management and clicking Retrieve Keys.