[rohrmann]

If your plug connection to the cable has pulled apart, it is also possible that you have had damage to the wire inside the cable, and possibly have a number of strands of the wire broken in either the neutral or one or both of the hot legs. This would cause a loss of voltage stability, and if the ground wire is broken, that would be your open ground problem. The plug should be replaced as soon as possible, before you can diagnose any other voltage problem.