I am new to Arduino and am just playing around with a couple of Nema 17 stepper motors. I have an Arduino Uno with a CNC shield. If I connect the Arduino with my USB everything is ok. When I connect the CNC shield after a couple of seconds the green light on the Arduino turns off and I lose my com port connection. I have a 12VDC 30 Amp power supply.
And of course you are going to provide a link to the specific shield and a schematic so we know how you have things hooked up so we do not have to guess am I right ?
Take a read HERE and come back to add whats missing.