Jumper cable connector melting

Why are you showing this picture here? Nobody can see where these wires go to. In one section, there appears a red, green and black wire. But the part you're holding in your hand has only green and black on one side of your hand, and the other side has red, green and black. So what's the deal with that?

It's possible that your arduino ground wire got shorted to USB 5V somehow. Possible.