Make sure the action is closed and locked up, use a knife tip or screwdriver to see if you can force the firing pin towards the rear, you need to release the tension on the firing pin as much as you can, with the barrel released the firing pin is jammed and the spring can't pull it back into the standing breech. If it's scoped you may have to remove it to get at the firing pin which is just ahead of the transfer bar, you'll see it after you cock the hammer. If that doesn't work, download Perklo's trigger info so you know how to remove the firing pin.
Tim