MusiCodes:
It worked, and then out of curiosity we switched the 221 ohm resistor with a 150 ohm resistor. When that did not work, we put the 221 ohm resistor back in, but the keyboard stopped working. What could have gone wrong?
Assuming you used the correct resistors ...... maybe connection came loose in the bread-board. Or maybe you plugged the resistor into the wrong socket on the bread-board. Check to see if the resistor's leg is going into the correct hole of the bread-board - so that the circuit is properly connected up.