[Newell Tank]

You didn't say whether the motor was running, only that it was "jammed". If it is running, did you try adjusting the tension on the drive wheels? Could be they're just slipping, but I'm not sure how you could "pull the cord out too far" and cause that. Nevertheless, if the drive wheels aren't clamping the cord enough, it will not move in or out, and perhaps if you accidentally stretched the cord out, you stressed the roller mechanism enough to affect the tension they put on the cord. On my Cablemaster model, tension adjustment is the yellow knob just above the motor. Perhaps your Neutral cam lever is released (the lockdown knob on the side, towards you from the motor); this allows manual "free wheel" use of the power cord, and may have accidentally popped up - it should be levered down to engage the drive.

You may have a different model than mine, but going here may help, and you may find your exact model with a little clicking around: http://www.glendinningprods.com/rlc.html