the audio in my home theatre system only works when we play a dvd… how do I sync the speakers to play when the television is on?
You should never be running audio from your TV to your home theatre system, because your TV is not meant to be an audio switcher. If possible, you should run everything, video and audio both, to your home theatre system first, and then send just one video cable out to your TV. The problem with most home theatre systems is that they don’t have enough inputs to do this with, unlike an actual home theatre receiver.
The safest solution is to run ALL audio directly to your home theatre system, and ALL video directly to your TV. This best suits the purpose for which each was built. If your HT system has any video inputs of the right connection (HDMI or component for HD video), by all means use them, and the video output from your HT system will then pass those to your TV for you.