Videos have sound, no picture
If there is sound and no video, this indicates a codec problem. For example, the file you open is an image file with mkv or mp4 extension. These file types can only be opened by installing the codec.
What is a codec?
What we call codec is derived from the words Compressor and Decompressor, meaning to compress and decompress. Avi formats called Divx are called in short and are actually a type of compression.
When you install a codec pack on your computer, your computer displays the video to you via the player through these codecs.
What is the action to be taken?
All you need to do is download and install a codec pack. The best in this regard is the K-lite codec pack. With GOM Player, you can open your video files without the need to install a codec pack.