This is more a hardware situation but there's no computer forum so this was the next closest thing.
I have an ASUS P4P 800 Se mother board in my mini arcade, and it worked fine for years. I took it out of the PC case and mounted it in the arcade and the sound stopped working. I messed with drivers for hours, searched high and low on the web. I found nothing nor did I get it working. In a rage I went over everything I had done in my head leading up to this point and the only thing I could come up with is the front audio ports had been removed as it was no longer in a PC case. "They would be wired in parallel" my inner voice said - but then again, not if the front doubled as a headphone jack that disconnected the speakers when the cans were inserted. I found the pins and dropped a pair of jumpers on them and the audio fired up right away.
Stupid design. There's nothing in the motherboard manual that says this needs to be connected for audio to work. I think that they should be wired in parallel and if you want to use headphones, you can turn the speakers off. Is this a common design?