The VGA cable only transmits a video signal.
In order to transmit sound from your PC to the TV you must have the PC audio cable connected. The PC audio cable is a standard 3.5mm audio jack on both ends. You can find this at many electronic stores.
After you connect the VGA cable from the PC to the TV you must connect the audio cable from the headphone jack on your PC to the audio input on the TV. Settings may need to be adjusted on the PC to control headphone jack sound. Please refer to your PC manufacture manual for more information.