The first step, you can do a simple check. For example, audio power, wiring is normal, chassis front or rear interface is normal. If everything is OK, you can proceed to the next step.
In the second step, open Device Manager and view the sound, video, and game controllers directory. Typically, you will find that the device is not displaying properly. As shown below, Realtek high Definition audio Normal, but the ATI HDMI Audio column is marked with a yellow exclamation mark.
The third step, to open the Driver wizard, recommended download the latest Driver Wizard Beta 2. Looking at "multimedia devices" under "Driver Update", the interface provides a complete list of drivers that can be updated. The following figure, Realtek Rui Yu hdmi audio driver version 2.55; Realtek HD Audio Audio driver version 2.57.
The fourth step is to download the new driver provided by the Installation Drive Wizard and restart the system after all the problems are solved.
The problem arises because the default driver provided by Windows 7 when the sound card is recognized is incomplete and lacks the HDMI portion. In the face of such problems, just use the Driver Wizard to detect and install the full sound card driver on the line!