Code will load and run once but not again

[gcjr]

@adopted01

However, when the Ardunio is disconnected and then promptly connected via another power supply, i.e. 9V power supply via the adaptor, the program does not run.

hopefully it clear how to externally power an Arduino (see Feeding power to Arduino)

i would try running a simple program, for example simply flashes the built-in LED (pin 13)