About motor shield v2.0 DC power

Hi, I am using Arduino Mega 2560 and motor shield v2.0 .

Now, I’m programming Arduino with Labview(it’s real time program)

The problem is that when I connect DC power(12V) while USB connected, my program stop, and PC cannot recognize the arduino.

I wonder why this happen.

Sorry about short English

Hi, I tested and plug the 12V into the J2 connetor, 12V to + and GND to - silk mark on the board. I also download the code from http://wiki.seeedstudio.com/Motor_Shield_V2.0/#software. it works well and the COM port does not drop. Please double confirm the 12v connection to +, NOT -. If the connection is correct, please help follow my hardware config to simulate and see if any issue. thanks.

Seeed techsupport team