Two days ago and yesterday the game was working fine, but when I started it today morning, all I saw was black screen, and the VO in task manager not responding... I don't know what to do. Can anybody help? I use win vista.

Seems like something unrelated to vo, did you change anything on your pc before vo stopped working?

nope, but shortly after I wrote that message everything went back to normal. Now I'm back here cause the problem is back :D

It sounds to me that there's a problem with your video card drivers or hardware. Perhaps something is overheating?