I have a lenovo thinkcentre m91p and want to connect to a older flatscreen Toshiba via a VGA cable and an audio cable?

The tv has the vga recepticle as well as the audio jack that l have connected to the tv, l plugged in the VGA to the rear of the Lenovo M91P desktop and the audio cable to either the audio jack at the rear of the computer or the jack on the face of the computer for the headphones. With this setup l am receiving the video to the tv but absolutely no sound from the tv. The headphone jacks on the computer work with my headphones but not with the tv. What am l doing wrong?