+1 on what Clive has to say.

Happened to me recently - I was using a cable clamp so it had me scratching my head for a bit - turned out I had an oversized blob of solder on one of my pins that shorted against the inside of the connector's sleeve. Was purely luck that it hadn't done that before - I'd recently moved my machine into a new workspace and had to unplug and re-assemble everything - something moved and I wasn't as lucky this time around... Made quite a pop!

Wal.