Hi, My Laptop Brand is Acer
Product name is Esxtensa 5220.
My Windows system is 7 Ultimate(64Bit)
I haven't installed any Adiou driver or software associated with Audio when I installed Windows 7 because when I have look at the Offical Acer website, I didn't find any Audio drivers listed for Windows 7(64Bit).
I am now having a problem not hearing a sound while only headphone is plugged. However, I am hearing a sound via speaker.
This is screen shot below shows that Headphone is plugged to my laptop.

This is screen shot below shows that Headphone is not plugged to my laptop.

This screen shot below shows that the audio device is detected well in the device manager.

This is screen shot below shows the the Audio preporties.

NOTE: Headphone is working well when plugging it to another HP laptop.
Should I install an Audio driver or software associated with Audio? If so, then where can I find them?
Any comments would be highly appreciated.