Instructions
Reboot your Xbox and turn it back on. If you made a recent upgrade to Windows 7, then the Xbox probably did not configure itself to the changes. Rebooting the Xbox will allow it to configure with any new plug-ins that were installed from the Windows upgrade.
Reinstall Windows Media Center. Access the "Start" menu and type "appwiz.cpl," then press "Enter." This will open the Programs and Features window. You can also access Programs and Features by going to the "Start" menu and clicking "Control Panel" and "Programs and Features."
Click the "Turn Windows features on or off" link located on the left of the screen. A Windows features box will open. Expand your "Media Features" by clicking the "+" sign. Uncheck the box next to Windows Media Center and press "Yes" to the warning that the uninstallation might affect other programs. Click "OK."
Reboot the PC. Navigate to "Start," "Control Panel" and "Programs and Features." Access the Media extender box using the same method previously. Check the box next to Windows Media Center (previously you unchecked this box). This will reinstall the program.