Maybe that little plunger lever latch on the lever is frozen and won't let it unlatch. You may be able to squirt some lubricant on it and then maybe see if you can depress it down with a nonmarring tool to see if it will unlatch the lever. Its located at the top rear portion of the trigger guard area at the top of the finger portion of the lever. If the lever is moving down any at all it is unlatching. If it is moving down any you may be able to insert a wooden dowel down the bore down to the breech face and tap on the end to move the bolt back. Maybe lubricate any points of movement on the lever and bolt also. Use a wood, plastic, or leather hammer to tap on the dowel and get one that is a close fit to the bore but slides freely. If you can get the lever to move down to the halfway position you should be able to remove the screw and the lever and then possibley slide the bolt out of the receiver over the cocked hammer and inspect the bolt, innards, lever, etc. for corrosion and lubricate the lever latch plunger and depress it numerous times till it is working freely. You may have to replace this part or re-radius it so it doesn't lock up so firmly..