Check the back of the DVD/VCR first to see if there are audio cables connected in the audio output. It's not hard to get them in the wrong jacks.
Next check the back of the TV to make sure that the audio connections are in the inputs that are associated with the video input that the DVD/VCR is connected.
Another possibility is that one some combo units there are different outputs for the VCR and DVD.
It's easy to make a mistake in hookups. A pro should have checked that everything worked properly before leaving.