I have a 686 in the shop now that has a damaged center pin ( that's the small rod that runs through the center of the ejector rod).
The head is bent beyond repair so it will need a new center pin.
I recommend you do not force the cylinder open, I believe that's what was tried with this gun.
If you are unsure as to what to do it might be best to take the gun to a smith in your area that's familar with S&W revolvers and let him take a look at it.
Regards
Bob Hunter
www.huntercustoms.com