Tractor Repair: transmission trouble, shift linkage, model tractor

Question
I have an IH 684 that while shifting from reverse to low gear the range lever stuck in the low position but tractor would not move although it seemed to want to. I also could not move the shifter. As I was on snow at time I had a neighbor drag me ahead about twenty feet. This freed up the shifter and I was able to find high gear where where it should have been in neutral. This was the only gear I could find. Does this sound like a diagnosable problem or something you might have heard of before and if so what would the fix be?

  Thanks for you time.

Answer
  Yes I've heard of it before.  I just answered a similar question on the same model tractor a couple of weeks ago.  Check the external shift linkage on the side of the transmission to see if you can get everything back to neutral, or if there is something stuck or broken.  If everything seems OK there, then there is a broken shift fork inside the transmission.