Please explain how i can do this. i have to go inside the computer?
I do not have any experience with your particular card, but I have read that drivers for the AGP ATI/AMD cards are a crap-shoot at best. Since your card supposedly has a sound chip built in to do exactly what you are asking (get sound over HDMI), you may have to provide audio a different way. Lets start by what brand of Radeon HD4670 you have. Then I can do some more research. I assume you tried Supermuncher85's suggestion?