My Acer Aspiron AO722 netbook give me a lot of problems.
My Internal microphone is working, when I connect an external microphone(headset) it still take input from internal one. In sound settings I can't see Line-in option in Inputs. But there is only Internal Microphone. I am using Ubuntu 12.04.
I don't have my AO722 in front of me to compare, but I suggest opening the "alsamixer" in terminal and check to see if you can mute the external mic. It's not a great fix, but for typical Skype in a quiet room use you can simply use the internal mic 100% of the time and your headset for sound. I expect you'll need to plug in the external mic first, then run alsamixer. Good luck.
