Arduino Mega not recognized by PC

I was using a Sainsmart Arduino Mega board connected to a RAMPS 1.4 3D printer shield. When I connected the shield to a 12v ATX power supply, it heated up and started to smell. I have completely removed the arduino from everything else, but now my computer does not recognize it, saying that it has malfunctioned. The on light is lit up, but the board won't show up on device manager. The light doesn't blink when I press reset.

Any idea what to do?

1176099:
saying that it has malfunctioned.

Probably true.