its been a long time I gave up on fixing the rear microphone jack on my motherboard (ASUS A8N-VM), problem actually was that by default motherboard is set to listen to front panel jack, which i have on my PC but i think its not linked to motherboard.
So to disable the front panel microphone jack and enable the rear jack, just double click the mini speaker in your system tray (right side of taskbar)
click advanced under microphone and uncheck "1 Front Panel Microphone"
That’s it you got your mic working.
If not, be sure that you have selected microphone in audio input option (in recording control)
man, i cant get it? my both front and rare mic are working at the same time. isnt it the same thing at ur end?