AC-97 front panel audio doesn't support jack detection, so it will need to select "Disable front panel jack detection" under Realtek audio utility.
After select this function, AC97's front audio should works properly.
For Windows XP system:
For Windows 7 system:
Select folder picture on upper right corner of Realtek HD Audio Manager utility, then check "Disable front panel jack detection" and click OK to finish setting.
