Thanks for the quick answer. I have actually sorted it out myself.
I went to:
NVIDIA Control Panel / Display / Change Resolution /( then your AV amp or TV highlighted as one of the display choices as it should be pluged in via the HDMI lead. For me it was my Onkyo amp.)
Then scroll up and change the Resolution from the PC menu your computer will be using to the HD SD selection that suits your TV or Projector.
After all this the AV amp recognized the HDMI input from the computer and sound played perfectly...