Desktop - LCD TV HDMI connection

Hello,

I have a really annoying problem, and I hope that someone could help. I've already googled it, but none of the normal suggestions for this problem solved it.

I've connected my desktop (windows vista, ATI 4770) to my Samsung 37" LCD TV trough a HDMI 1.3 cable.
The video is excellent, but there is no sound coming out of my TV speakers. I've set my desktop sound device to "High definition audio", the sound device added to my computer after i installed the 4770 graphics card (so I know the graphics card supports sound), but nothing.

The sound in other HD devices I have works just fine with only an HDMI cable. I've tried all 3 HDMI connections in my TV, but with no success.

Thanks a lot for any help or advice!! this thing is driving me crazy...

Michael.

Configuration: Windows Vista
Firefox 3.0.11
ATI 4770