Apple wired keyboard randomly works with Aluminum Macbook

I've got an aluminum macbook running 10.6.8. I normally run it in clamshell mode when I'm at work, obviously plugged into an external monitor and keyboard.

Randomly it seems, the external keyboard will not work. At all. I reset the computer, try different combinations of plugging the keyboard in before the power, after the power, in between the power and the monitor.... no dice.

I've done PRAM and SMC resets.... no dice.

I pop the cover open and the integrated keyboard works fine.

Some mornings, I come in and plug in, keyboard works fine. A little later I grab the laptop to head to the lab, come back, keyboard is dead.

Other mornings it just doesn't work when I show up.

Keyboard works fine in other computers. Other keyboards work fine with this computer.

What's up?