Go to Homer's bedroom and click on Homer's desk, on the bottom right corner of the screen. After that, click on the right drawer and you should be able to pick up and keep a note. Go to the nuclear power plant and go to Sector 7G. You should now be able to pull the lever on the wall in the upper left part of the screen. A rope will fall -- pull it. Turn the light as it appears. Finally, get the donuts.
