which case do you have? That board does not even have a seperate socket for AC97 so it is a universal.
In the bios is Front Panel Control set to Auto?
In Realtek Audio Manage is Front Panel Jack Detection set to Auto or Enabled?
Are you sure you didnt plug in the cases AC97 into the hd-audio socket?
My case is a Rosewill Blackbone http://www.newegg.ca/Product/Product.aspx?Item=N82E16811147023&Tpk=rosewill%20blackbone
I plugged the HD AUDIO from the case to the HD AUDIO on the board :O
I believe the Mobo is not detecting the HD AUDIO because in BIOS, HD AUDIO is set to AUTO, with no option for ENABLED.