VLC might have issues with the playback because of compatibility with the codecs or the lack of codecs, but this is rather unusual to happen since VLC is known to support all the video formats there are except the proprietary ones. If you believe this is an error with the software, reinstall it as it's available and updated to support new features, but if the video file is corrupted, then you have to acquire it again.
In most of the cases, when only the Audio is playing, there are no available video decoders to decode the image.