FYI, did you know that for CNC use, other than three unused transistors (FETs) and a few LEDs, the RAMPS board is really just a connector between the Arduino and the stepper drivers? It also has a few convenient pins and connectors. See the schematic – http://reprap.org/mediawiki/images/f/f6/RAMPS1.4schematic.png from http://reprap.org/wiki/RAMPS_1.4 .
You probably shorted power and ground. What smoked?