Thanks for your willingness to help, but I have stumbled onto the answer to my problem. I removed all of my batteries to test them (I thought perhaps as the inner plastic piece was laying around it may have come in contact with a peice of metal (like the foil back on the circuit board) and drained my batteries (this did seem very unlikely)). When I put the back it worked. Although I still have no clue what I did to cause the problem, I must have reset the calculator - so it is now working very well.Thanks, Clint Law