Vista Media Center can't play video

Hi, I am trying to connect my Vista based PC with Media Center to my Xbox 360
to view my videos. Somehow when I go into Media Center in Xbox 360, click on
a video, it doesn't do anything, just highlight it (enlarged the thumbnail).

I went back to my Vista PC, launch Media Center, click on a video, it does
the same thing, even the sample videos preloaded in Vista doesn't play, just
highlighted.

What am I doing wrong? When I had Windows XP Media Center version, there
were no problems watching videos on Xbox 360 or Media Center on PC. But
switched to Vista, can't get Media Center to work properly. Do I need to
upgrade anything?

Thanks.