my sound was broken and there was nothing broken with my hardware, after a long time i searched a solution and finaly i found it. now i want to share the software that installed the sound driver again.
my laptop is an acer aspire 8930, the driver is named:
Realtek ALC268 ALC885 ALC889 v6 0 1 5618
unrar and open setup. the instal wil start and you will have sound again!!