I am a new user of Directory Opus.
When I am clicking on a .VOB file the movie is playing in the Viewer Pane.
But I can not hear the sound of the movie.
.VOB's are usually DVDs. DVDs are usually AC3 audio encoded. I'd install AC3Filter so it can decode the audio.
ac3filter.net/wiki/Download_AC3Filter
(This was written at the same time as ktbcrash's reply, above, so there is some duplication/overlap.)
You may need to install (or just re-register) an audio codec for whichever audio format is being used by the .VOB file (usually MPEG-2, AC3 or DTS).
FFDShow is a good bet, as it can decode just about anything and is fairly self-contained.
Note that 64-bit Opus requires 64-bit codecs, so be sure to get the 64-bit version of FFDShow if you decide to try that. (On the other hand, most other video software is 32-bit and uses 32-bit codecs, which can account for some differences between Opus and other tools when playing videos.)
Links to FFDShow and other information can be found here: HOW TO: Enable/fix playback of various media formats in Opus.