Unable to hear the sound in my Acer Laptop

Question

Hi I am having acer Aspire 4920 notebook and suddenly 2 days back i am unable to hear any sound in the laptop. the volume level is high and the speaker volume control is not in mute. checked the device manager- audio device, its installed and status is working properly. don't know how to fix the problem, can you pls suggest me a solution for the above problem