Sadly it is a limitation of Microsoft Windows 7 Media Center. Even though DisplayPort 1.1 and 1.2 are technically capable of HDCP and your graphic card and display support it, Windows 7 Media Center does not. See http://support.microsoft.com/kb/2392252 for more information.
If it is Copy-Freely content you can restore and then maximize Windows Media Center and it will play but not Copy-Once or higher.
