HDMI no sound

[fredca]

I have a Bravia KDL-32S3000 which I want to connect to my pc using HDMI.

The first time I plugged the PC into the HDMI socket with the TV on the TV switched automatically when it detected the connectiopn. I then played a movie and both picture, 1920x1080i, and sound played well.

I unpluged the PC and when I went back the Bravia didn't automatically detect it but when I choose AV7 the video played but no sound?

I have the PC and Sky HD+ connected via HDMI so I unplugged the Sky box and when re-inserted video OK but no sound so I powered everything OFF by disconnecting the mains supply and back on a few seconds later Sky fine but still no sound from PC. I scanned for HDMI connections and the Bravia said it din't have any! it was still playing the SKY programme and video from the PC.

Anyone any ideas?