I’m new in arduiono. studied the blogs and documentation. I have a arduino Mega2560 Rev3. I first loaded a simple sketch to the arduino without a shield. The sketch works fine. Then I connectetd an ethernet shield. I loaded a sketch that is initializing the ethernet shield and works with it. After loading the programm it works fine.Then I disconnected the usb from arduino and connected it to an external power supply. The sketch doesn’t work. The ethernet shield will not be initialized.
I also tried to connect RX0 to TX0 pin, but it doesn’t solve the problem.
I don’t know, how to solve the problem. Pleas advice