It is possible to select a source with a Yamaha and have the wrong audio mode.

First, the receiver's display should read AUTO a few seconds after you select each device that has a digital input. If it says ANALOG and all you have is an optical cable, you will get no sound. If it says DTS and you have the right digital connection but no DTS sound track, it is again silent. Auto lets it select whatever the heck audio it is getting.

In fact, I always back up the digital connection with analog wiring just in case. I actually ran across a track on a Toshiba Demo DVD a few years ago that put out no digital signal, just an analog one! And this is of course necessary for a two-zone situation.

It might also be that you are plugged into the wrong digital input or that the digital input has been assigned to a different input via the menu.

As for no picture, you will get no picture if green is not connected properly. If only green is connected, you will get a black and white picture. If green plus one color is connected, well, you get a sense for which color is missing by the resulting color. If red and blue are reversed, the picture usually is REALLY BLUE.

Any of this hit the mark?