When we play a DVD, the sound on our Sony TV works, but when we try to just listen to the actual cable TV, we get no sound. Any ideas how to fix this, it was just working yesterday...

How is the Sony connected to the DVD and how is it connected to the cable?

Check the connections to make sure they're all there and inserted tightly.

Sometimes the connection from the cable box includes cables to carry the video and separate cables for the audio. Do you have an HD set or an older analog set? DVDs usually have one cable for video and two cables for audio.