Don't know why you are wasting your time with a Casio -- if it were a HP-41, -42 or -67 well then they still sell good, now that is a programmable calculator!
I've brought back a few 1980's era devices to life, often you just need to be persistent
Start here...
http://www.rskey.org/casio.asp
Things to try...
Identify which Casio programmable calculator you have. You want the model number eg FX-780P. Maybe you have to peel off the COMPUNAV badge. Maybe turn the calculator over and look at its data plate or look in the battery compartment.
Do that and come back here, see what we can get for you.
Before you get too excited, check that the batteries did not leak after they went flat.
Any green corrosion on the battery terminals (easy to spot) or elsewhere (not so easy) and you may have a dead duck.