My GF got ASUS X55A and had same problem. Just Video, no Audio from HDMI port. I solved it in two steps:
uninstall driver in "add/remove programs" software for audio drivers called "Via..." and then I installed Realteck audio soft for audio driversYou can comfortly identificate your sound driver by:
- go into the "device manager"
- then go into the "properties" of the driver...
- click on the tab "specifics" and here change "description of the device" into the
"identification of the hardware"
- copy there the first title (it must look like this "HDAUDIO\FUNC_01&VEN_8086&DEV_2806&SUBSYS_80860101&REV_1000)...
- paste it into the web browser and some pages will tell you what is it and what driver is for this device. (my recommendation is realtek for audio drivers) (and also u can easiely identify every device and driver for them thru this procedure.
that was first step... if you got realtek soft installed, first step is not needed.
is reinstall one of the "Sound, game and video controllers" and its called (I translated it from my language of windows) " Intel (R) Voice for dysplays"
- go to "properties"
- go to tab "driver"
- click on "backup changes of the driver"
- and then "actualize driver"
At the end try to connect HDMI and test it if it is working. GL HF ;oD