This is a big problem for some people when connecting there computer and TV via HDMI you can see the picture but there is no sound. In the device manager it might show your TV as a generic monitor thats fine and should not effect the sound output. Follow these steps to get full sound over HDMI

Goto control panel
Select sound devices
Click on the playback tab
Now this is the important step people overlook
Right click in the blank space under the working devices
Tick show disabled devices and disconnected devices
Can you see your HDMI device? Mine is a Samsung TV
Now right click on the HDMI device and set as default device.

Now you should have sound

I hope this helps you guys out.