I have a question for you Rav0506 . Since you wrote your comment on 9/24/14 have you ever: 1) had the 12v lines connected to your ramps board and have your computer plugged into the arduino usb connector at the same time you were connected with the 5vsb to the vcc pin and the ps-on pin on the ramps board with no ill affects to boards or computer with the computer connected and on and the atx poweby new3der - RAMPS Electronics