I use WindowsXP and I have recently installed a second ATI card. Ever since then my sound has randomly stopped working. Occasionally it will set my Default Playback Device to "ATI HD rear audio output", which I fix on my own with no problems, but it has also stopped working without changing the Playback Device. This is fixed after restarting my computer.
If it helps any, I can still always hear my mic in my speakers when the sound isn't working.

Halp?