Irritating HDMI audio question

[SCRawl]

Up until recently I've been running my computer and TV in a DualView display scheme. My computer (an HP with a 7600GS HDMI video card) is connected with my LCD TV via a lengthy HDMI cable, effectively extending the desktop to the TV. I was able to get sound through the HDMI cable to the TV, and, say, watch movies on the TV in this manner. Last week I had to disassemble the computer in order to install a second hard drive, and when I plugged it in again nothing worked. I got the video working again, without much effort, but the sound won't work now.

I recall vaguely that this was a problem I'd had in the past, and that I'd managed to lick it then. No such luck this time: either I'm dumber than I was a year ago, or the problem has changed. I did have an RCA cable going from one plug to another (don't know which anymore) at the back of the computer, but I can't see why that would make a difference for this problem.

Any thoughts?

[Starglider]

Firstly as I recall Nvidia cards have an analogue audio input and need to be connected to your motherboard's audio header with a cable to encode the sound into the HDMI feed (ATI cards have an internal audio codec). If your card has an audio input, check that it's connected to your motherboard (securely, those little push-pin connectors come loose easily).

Secondly if your video card has an extra power connector, check that it's actually connected to the PSU. Causing a modern graphics card to run with PCI-E bus power alone when it's designed to draw from a direct PSU feed can cause bizarre intermittent problems.

[SCRawl]

Firstly as I recall Nvidia cards have an analogue audio input and need to be connected to your motherboard's audio header with a cable to encode the sound into the HDMI feed (ATI cards have an internal audio codec). If your card has an audio input, check that it's connected to your motherboard (securely, those little push-pin connectors come loose easily).

Secondly if your video card has an extra power connector, check that it's actually connected to the PSU. Causing a modern graphics card to run with PCI-E bus power alone when it's designed to draw from a direct PSU feed can cause bizarre intermittent problems.

Your suggestions got me thinking again, which is usually a good thing. I checked out the box that the video card came in, and found that the RCA jack that I thought was video output was actually RCA audio input. I connected that with the digital audio output -- by way of the RCA cable I mentioned the first time -- and presto, we're back in business, all externally.

Thanks for starting me in the right direction.