ECS GF8200A HDMI, Sound problems

I used one of these boards today for an HTPC build and everything went great, until I went to watch TV. I cannot figure this one out.

My sound works fine as long as i'm looking at something SD, playing music, etc. The second I go to watch an HD video on YouTube, the sound no longer works. The sound also does not work when using the TV tuner. It's almost as if the HDMI is not carrying the audio. Is this possible? How can it be fixed?

I should add that this system is running Vista Ultimate 64. Specs below.


My HTPC specs:

ECS BLACK SERIES GF8200A (V1.0) AM2+/AM3 NVIDIA GeForce 8200 HDMI ATX AMD Motherboard - Retail

AMD Athlon II X4 620 Propus 2.6GHz Socket AM3 95W Quad-Core Processor Model ADX620WFGIBOX - Retail

DIAMOND ATI TV Wonder HD 600 TVW600PCI PCI Interface - Retail

WINTEC AMPX 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model 3AXT6400C5-4096K - Retail51965536

SAMSUNG Spinpoint F3 HD502HJ 500GB 7200 RPM SATA 3.0Gb/s 3.5" Internal Hard Drive - OEM51552891

Rosewill R223-P-BK 120mm Fan ATX Mid Tower Computer Case - Retail51965536

Hanns·G HH-251HPB Black 24.6" 2ms HDMI Widescreen LCD Monitor - Retail51853106