No DVD Sound

I have a new Yamaha RX-V1600 with a Panasonic 42" plasma and Sony DVP NS315 DVD player. Everything works fine (TV , satellite subs, SWFR & Receiver) on 2 channel except I can't get sound out of my DVD player. Optical cable is used from HDTV box to the receiver for the TV and digital cable is used from DVD player to the receiver. I've tried all input modes from the Yamaha receiver and still no sound. Any ideas out there?
Try going into the menus on the Sony player and make sure the digital output is setup properly. It's usually turned on and you have to go into the menus to turn it off, but in your case maybe somebody already did this.
I would check the outputs of the dvd player. Analog, digital, optical out or digital coax. I have a Yamaha dvd player and it can get real anal on me sometimes when changing from dvd audio and 2 channel audio. In some cases I have to put a dvd disc in the player to change from dvd audio to analog audio. Also in my case I must have the TV on and the OSD on to see what I'm doing. I don't know what type of player you have so this may or may not help good luck

Oops, I see your using a Sony player. Anyway the result is the same. As Jfacker says check the output menus on the Sony.