Meg93931:
Sorry. I will try to explain better.Say the Arduino was running a mini LED screen and then the Arduino was unplugged from the computer and so the Arduino had no power and the LED screen had no power. And then you plug in the Arduino again, so they both get power again. The Arduino stops printing to the screen. It only starts again if I upload the code to the Arduino again, or if I open the serial monitor on the computer. How do I get the Arduino to keep printing to the screen on power up?
After disconnecting the power, the Arduino will never continue from where it left off when the power was cut. It will always start from the beginning, the 'setup()' function.
But it sounds like this isn't really what you want to know.
So on power-up, nothing is printed to the LED display, despite the fact that everything was fine immediately after uploading the code?
Effectively, powering up both should do the same thing that happens at the end of an upload.
When you power up again, instead of re-uploading the code or opening the serial monitor, try pressing the Arduino's RST button then releasing it and see if the Arduino prints to the display as it's supposed to.
Let me know what happens.