I am having this same issue, but its been going on nearly two years since I bought this computer. It seems to be intermitent. I've uninstalled and reinstalled the driver. If I put a set of headphones into the jack, the built in speakers start to work. with no headphones- no sound. Sound typically works with HDMI out but sometimes I need to click on playback devices and select the HDMI manually.
HP Pavilion dv6 Notebook PC, LY079UA#ABC, Windows 7 Professional 64-bit Service Pack 1,Audio device 1: IDT High Definition Audio CODEC, audio device 2: Intel(R) Display Audio
Please help, just want the laptop to work properly