I have a motherboard with the ATI 4290 built in. I use HDMI out to an A/V receiver. I've had sound before, but the past few times I've started up, ATI Catalyst pops up a message saying a DVI->HDMI connection has been detected, even though it's plugged in HDMI->HDMI. Therefore, I'm not able to get sound. What's going on here?
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Try force TV detect in the Catalyst control panel. Or go to AMD's site and download the latest Catalyst drivers.