this might be a stupid question, but I just started with Arduino. I want to control a 12V pump with an Arduino and I want to use the power source for this pump for the Arduino as well. But when I connect the 12V to the Arduino using the pins on the board, the program seems not to be executed. Nothing happens. When I connect the USB the program runs fine. I also tried the power connector without luck. In all cases the power led on the board is on. What is the problem?