If you only connect the HDMI cable, no other cables are required. Then set your TV to view the HDMI (not PC) input and it should work. Using VGA and HMDI may be causing it not to use HDMI which transmits sound and picture.
Alternatively, by your VGA connector on the TV, there should be a small plug like a headphone port perhaps with PC audio or some symbol next to it (may require the manual). If you own a double-ended audio cable (ie: has a plug like your headphones on each end) you can plug one end into the green socket on your laptop and the other into this port on the TV.