Foxconn g31mxp front panel Audio not work

Go here to access information on your motherboard. Included there are links to the manual, which describes the F_Audio port pins. You have to compare the pins there with those on your unnamed case and adapt them if needed.
http://www.foxconnchannel.com/prod [...] -us0000416

This is the link directly to the manual:
http://www.foxconnsupport.com/down [...] d%20Manual

The pins are described on page 15 of your manual

Thanks mongox,But i cant compare that pin configuration with front panel board.because it is no named,it's wire ends marked as FR_R, FR_L, RR_R, RR_L, MIC POWER, GND, MIC_IN.
Then how connect them.
are there any jumper setings related to F_AUDIO ?
plz help me further.

It's very likely that if the front panel is designed for HD audio - and some are designed for AC'97 - then it will plug right into the 10pin header you have.

Does it only have nine wires? Is the empty place over pin8? If so, you're likely just fine plugging it in.

Here are two Front Audio plugs, despite the different names, they are the same. Yours is the first one listed.

Note the following. It shows a HD Audio pinout compared to a AC'97 pinout. Sounds like your front panel of the case is using AC'97. Your motherboard only supports the newer HD_Audio.

I do not know if a front panel wiring from the case designed for AC'97 will work properly with HD Audio. Your case may also include two different wiring harnesses.

Notice how closely what you describe fits the AC'97 pins!
Note the above graphic and instructions are NOT about your motherboard.