So I plug in my headphones last night...

[salloch]

and the sound from my speakers gets muted, as it should. But then, I don't get any sound from my headphones. Uh oh. Now, when I unplug my headphones from the pc, I can't get any sound.
I've triple checked every volume control, etc... but no luck. I know there is some mechanism by which your speakers get "muted" when you plug headphones in, and this appears to be permanently tripped, although without being able to get sound from the headphone jack.

I also tried plugging the speakers into the headphone jack, but still no sound.

Any ideas?