Thank you very much, man.  Thanks a lot! 

Not a long time my friend told me a command for RUN menu and when I open this application there were many things and one of them was WINDOWS AUDIO. When I clicked on Windows Audio I saw three falling menus in which I had to set "Restart system if... (something)". And when I did this setting then, my sound disappeared no more. So, can you tell me this short command if somebody understands or supposes what I am talkin' about?

P.S. It's not regedt like some people have told me already.