HDMI audio from computer trouble

Hello,

I'm ridiculously new at this so I apologize. I've hired AV guys to try to fix this problem but nobody knows how.

Here's the problem:

I have a pc running Windows 7 with a NVIDIA GeForce GT 520 Graphics card. When I first hooked it up I did so into an Integra receiver and sound worked fine.

Then I had an AV guy come to hook up a 4x4 matrix and not only did the sound stop working through the matrix but when I tried to hook the hdmi cable directly into the receiver that didn't work all of a sudden. When you look at the hardware icon, it says that there are no speakers hooked up.

I've tried plugging it into different inputs on the same receiver and on a different receiver (Onkyo). I've tried different cables. No sound on any of them. However I did get sound when I brought the computer in to memory express and they tested it by bypassing a receiver and plugging hdmi directly into a tv.

I've gone through two sets of home automation experts and they have no clue. I'm not much of a tech when it comes to this stuff and I would be very grateful for any help you give.

Thank you

The guy didn't know how to fix it. Video works fine although downgrades from 1080p to 720p when you plug into the matrix. (all other inputs into matrix are 1080p) I guess I'd be thrilled if I could get it working directly into the receiver again and then I'll try troubleshooting the matrix system once I have an audio signal.

W.r.t. to the EDID thing, I read the articles you've posted but its all a little bit beyond me. Is there something I can do to test this?

Thanks again,

D