With the display facing down then you will see that in the center of the circuit board are two small raised posts about half an inch apart - they look like part of the circuit. With the power on touch a screwdriver or nail across both posts at the same time. Without doing this step none of the buttons will do anything after replacing the batteries. The pictures on this page don't look like the insides of my calculator though, and I cannot see these posts here.
I dont see any raised posts to short out on my circuit board, where are they? My circuit board says to do that yet doesnt show you which posts to short out. My batteries are replaced but as you say, the buttons are now doing nothing.
Nice post! My batteries just gave up after 15 years. This whole time I tht it was a solor calc, LOL! Thanks for the easy instructions.