Please test your DEll XPS 2720 mic audio jack and let me know the result

If you own Dell xps 2720, please plug your mic in the mic input jack on the lower left side.  Please tell me if yours pops up a dialog box asking you to choose the corresponding input you've just made.

If I plug in my headphone in the stereo out jack, it will pop up a dialog box asking me to choose the type of device I've just plugged in (i.e headphone, headset ect. )  However it doesn't pop up that dialog when I plug the mic in.  Could it a hardware failure?

I have uninstall audio driver and reinstall it so many times but the problem still exists.  Please tell me what yours does when you plug a mic in.  Thanks