Before going too far I would double check that the power supply cable hasn't shorted out. A simple volt meter would work for that. Those cheap cables and cheaper connectors are notorious for breaking, especially if somone yanked or stepped on it like you said. If that's OK I would check the circuit board near the power plug with a magnifying glass to make sure no traces were damaged or the board cracked. If that looks ok, use the magnifying glass to see if the leads from the plug broke out of the solder or broke out of the plug. If it's the former you can easilly resolder it. If it's the latter you will need a new plug, or, if you're like me, you take the plug out altogether, cut the end off the power supply cable, push it through the hole and solder it directly to the board.