Hrm, myself and one of my friends had this problem. It turned out that if we both installed OGG support, then no one could have voice over google talk, but video worked. If only one of us had OGG support installed, then we could have voice. It was quite a weird bug/solution to the voice problem I had.

However, if you said you reflashed it, and still had the problem. I doubt that OGG support is what's causing you not to have sound.