Sony bravia to my P/C

You need to wire up the audio from the computer.
The 15 pin cable is only the video, next to the input on the tv should be a red and white phono connector which should say audio or line in, get a cable that has a headphone type jack on one end and 2 phono red and white plugs, connect the headphone jack into the back of the pc, should be the green audio out where you would usually connect pc speakers, then the phono plugs into the back of the tv and insert them into the phono ports on the back of the tv that say line or audio in. Turn the TV to PC and thats it.

hope this helps