No sound with HDMI
I had the same problem with a Sony VAIO VGN-NW270F laptop connected to a 32-inch HDTV (also Sony) and I nosed around and stumbled onto the solution. Maybe it will work for you. Start with both TV and computer turned off. Make the HDMI cable connection. Turn on the TV and choose the HDMI input for the port you connected to. Turn on the laptop and do what you did to get the computer screen to appear on the TV. (I believe you said this was done successfully.) Then look at the notification area (lower right) on the laptop screen and click on the "Show hidden icons" symbol. (Any wonder you didn't find it?) Mouse over the hidden icons and find one that says HDMI. You won't find it unless the cable is connected and you turned on the TV and computer as described. Then double click on the HDMI icon. A box will appear with two audio devices in it. The Microsoft one will be selected as the default. Highlight the other one and click on "Set default" below the pictures. OK the box and Voila! Glorious sound from your TV speakers.