Homegroup Sharing won't see new files

Hi all.... noob here, hoping I can get an answer. I've got Windows 7 set up with a homegroup, and have shared a video folder, viewable through a media box connected to the TV. The media box sees, and can connect, to the shared folder on the desktop, and can see, and play, the content that was there when I set up the media box. However, when I add new files to the shared folder on the...