There are two tiny metal "tabs" or fingers in the arduino-nano mini-USB socket that can get hooked into the plug when it is first inserted (has happened to two different Chinese made nanos in our club). This will prevent the plug from going in far enough to make contact. They must be carefully pried up out of the way (don't accidentally hook one of the contact springy wires in the socket). Usually if you can get the plug to properly go in once, the little fingers will be bent up enough and won't cause further problems.
AL? VE3RRD
N8DAH
Dan Reynolds