Try pressing the "copy" button and then the black "start" button. I did this a couple of times and the printer started working again.
Other people have had success when they open the lid, pull down the gate (to expose the cartridges) and then push in the little button on the left (to fool the printer into thinking the lid is closed). With that button pushed in, try pressing the "copy" button and then the black "start" button. The printer will make some working noises. When you close everything up again, it should work.
mynameiskurt, October 2008