I'm having the same problem as mac was, only on one computer in our lab. The other three seem to work fine.
With Enhanced Video on, sometimes it plays fine, and sometimes it plays only the audio. With Enhanced Video off, it plays nothing at all.
The way our experiment is structured provides ample little test files- questionnaires with an instruction page, then the video- and it performs the same on each of these. It performs the same with every video I try, all 5 of our stimuli and WMV test videos. All of these are in WMV format.
We're running Vista, WMP11 and MediaLab 2008.1.33. Also, I find that if I hit ctrl-alt-del while the video is running, then cancel, the video displays where there once was a black screen.
Any help?