In the latest versions of operating systems are the default drivers that are designed to work on the architecture of HD Audio. So if you after use, for example, Windows XP SP2 installed Windows 7 and found that the connectors for headphones and microphone on the front panel stopped working, it is likely that this is the reason. However, before proceeding to solving the problem at the level of the motherboard, try to eliminate it by means of the OS. First, make sure that you have installed the Realtec driver, which can work not only with the "native" format AC'97, but with HD Audio. Secondly, try to disable in the settings control panel, Realtec the option auto-detect front panel - this is often enough to solve the problem.
If the measures outlined in the first step, if that fails, look for the switch AC'97 / HD Audio in the settings of the underlying system I/o - BIOS. To do this, from the main menu system to initiate the restart the computer and press the Delete key or F2 after the start of a new load cycle. Some of the computers to log into the control panel settings BIOS used other combinations, so in case of failure of these keys, specify a valid combination in the description of your version of base system of input/output. Often it is possible to learn from the inscription that the boot process appears in the lower left corner of the screen.
Panel BIOS settings, find the line with the setting belonging to the front panel. For example, in versions of AMI company, it can be placed on the Advanced tab, and formulated as the Front Panel Type. Change the value in this row - if the panel connectors are not working when set to HD Audio, change it to AC'97 or Vice versa. Then exit the BIOS, saving the changes. If the desired settings do not appear in your version of the base system, it is possible that the switching is done mechanically, with a jumper on the motherboard.