Which end isn't unlaching? If the back lifts after you pull the ring thingy and its the key that wont turn you have a couple of options. First try the fist in the seat as mentioned above. If that doesn't work, the cable from the key lock may have come unseated. This happened to me. Only way to get it off is the pry the seat up - don't worry, you can almost bend them over without damage so use plenty of force - until you can get a screw driver in to push the latch that the key normally operates. Took me hours to get this done but I had no idea what I was doing. It would help if you can take a look at one to see which way you need to go in, what to push and which direction. Maybe someone could post a pic - I can't just now as I have to go to work.
If this gets it off you need to relocate the cable and then tie it in place with a small cable tie so it won't happen again.
Same thing could have happened with the ring pull.
Good luck.
Welcome to the site by the way.