This solution that worked for me and i’m using Windows 7:
Uninstall Quicktime 7.7.2 and reinstall the older version 7.7.1, here’s the link for it:
You'd have to find out what codecs are being used in the video file. Apparently the video one is not being supported by QuickTime but the audio portion is? If you go to QuickTime Player menu > movie inspector it should show what codecs are being used. If you want to post them back and what ext. is being used in the file, someone here may have further info.
Also as an example, DivX format is not supported by QuickTime for windows, yet it is with QT for Mac. And what you describe with black screen for video, but having audio, is exactly what I've seen in the past with in this particular format. I'm not saying with certainty the file you have is a DivX.