Hi,
Thanks for your comment. There is no serial monitor to open. It's the same laptop that sent the code to the Arduino in the first place. To be sure, the serial.print data is going the other way, but there's handshaking going on regardless of the flow of data and there's no indication that the Arduino isn't listening when the sketch is being loaded. The puzzling to me is that it used to work and now it doesn't 
Raoul