If you can get something to hold the other side (the bits that come out when you pull the rope to engage the to the crank) it will undo, there is a specialised tool available for this but I have been succsessfull with just a vice and socket before.
May-be your spring is broken,i repaired a honda in which the pull rope broke half way out,in doing so the recoil spring inside sprung back with such force it snapped...ken
If when you try to tension the spring by turning it clockwise without the rope in it and all you can gear is scraping around and no tension builds up, Generally you are best to get a good second hand recoil or replace the spring and reel.