mkv video files have only sound no picture

Hello there.

I searched the posted topics and I have noticed that some other people have also trouble with this.

The player on .mkv Video files only plays the audio stream, no video. There is an error message: "Unknown file Format (RV40).

I have installed the Matroska_Pack_Full_v1.0.2 as some people have suggested but still the same problem.

I am not having problems with other video files.

OS Win98SE, PIII 550

Any hellp will be appreciated.

Thanks

john 8)