Why I can't get signal through S/PDIF from mixing board ?

I recently changed computer, while nothing else (outboard) has changed or even ''moved''.
 
Here's my setup :
 
PC with Frontier Design Dakota ADAT card connected to Yamaha console (02R) (ADAT multichannel)
Stereo output from console sent back to Dakota through S/PDIF (which I use for mixdown)
 
Sonar 8.5
 
I always used that setup in the past, no problem.
 
I was able to record multiple tracks (first prohect with this new PC) - Windows 7 x64, then I tried to mixdown tonight : I do not get signal back from s/pdif (nothing, flat line in Sonar).  I am trying to figure out what happened, but I'm out of ideas.  I unplugged that cable from computer to make sure it was reconnected properly.  Checked that connection was physically ok on the other end (console).  Nothing : can't mixdown anymore !!
 
What am I missing ? what ''plumbing'' may i have forgotten to check ?  Going nuts !!...
 
Thanks,
Rob