help me ?

Hello
I have recently 1 Arduino AT mega Uno R3 ELEGOO 320P
it is connected to the USB port of the pc and to the power supply 5 v
I just realized a little program with arduin and Ldc1602
the compilation is done without worry.

When I remove the USB cable the arduino is powering the Lcd too but more program
If I reconnect the Usb port the program works

What I forgot to do

Thank you for your help
Exolite

What I forgot to do

Read this, in particular points 6 to 11. It will explain what you need to do so that we will be able to help you.