Hey there @Psilent,
Please give a try to repairing the client and let us know if it helps! To do this, close the game and open up the launcher. Click on Game Options just above the news section and select Repair from the drop-down. Once it has completed repairing, launch the game and let us know if the sound returns.
So it's still...@Psilent?
Bad joke. Moving on.
The sound options in the game take place after the first two logo screens play, which means the issue may be with the in-game settings. When you're at the log in screen, select Settings on the left and check the volume options in the Audio section. Ensure that the Master Volume is turned all the way up, as well as the individual sound options.
EDIT: Pressed post too soon