Providing electricity to Arduino via VIN

Hey all,
I have weird problem. I'm triggering a stepper motor via DRV8825 driver chip on a breadboard. Everything runs swimmingly, electricity is provided by a 12V, 2.4A DC adapter connected to VIN/GND on the Arduino. If the program is running and I disconnect the USB, everything still runs as planned.

However, if I start up the Arduino without the USB connected, the motor just makes sad little noises as if not getting enough current, maybe. Plugging the USB in For just a moment starts the program and everything works fine.

Is this a known issue? Do I have to tell the Arduino where to get its current?

Thanks for your thoughts,

A schematic would be much appreciated even if hand drawn along with the sketch you are using.

Could you also take a few moments to Learn How To Use The Forum.
It will help you get the best out of the forum in the future.
Other general help and troubleshooting advice can be found here.

I'm going to guess that somewhere in setup you have a while loop that waits for the serial port.