With our grinder, the buttons for 4,8,10,12 cups seemed to simply do nothing. It turns out that the shut-off button (top center) had jammed. Although I managed to get the button out of its cockeyed position, the grinder still didn't work.
Step 1: Remove the beans
Step 2: Remove the controls
Step 3: Inspect the buttons
I looked at each of the four buttons at the bottom, and there was very little gap between the outer button and the inside posts. I could see the "grind" buttons working correctly as I pushed each of them. However, the shut-off button was indeed stuck! The post was sort of stuck in the down position.
Step 4: Gently pop up
Now, just like the cardinal rule of working on the internals of your computer: don't be overconfident; test your changes now, and don't be cocky, putting everything back together before you know for sure.
Plug the grinder in and push the "4-cup" grind button. It should buzz to life. Hit the shut-off button now, gently, so it doesn't jam.
Step 5: Replacing the controls
Get back on that horse and brew some heaven!