In order to find out, what may be wrong with your video, you can use the following three applications to analyse the video file.
When done, you can use the "Report" (VideoSpec) and "Export" (Media Inspector) button to export a report,
attachable to your next post via the Image button.
In MediaInfo you have to go to the Menu Bar, select View > Text and copy the text via CMD+A > CMD+C and paste it via CMD+V into your next post.
If it is a WMV file, either use VLC Player or
Movist or install Flip4Mac to play that file in QT Player.