Is the lever opening 1/2 an inch or is the bolt moving back half an inch?
If the bolt is not moving, have a look at the left side, there are 4 screws on there. Try loosening the uppermost screw (the medium one, near the top edge of the receiver) one turn and see if that does it. On mine that screw was too long from the factory and rubbed against the bolt, preventing it from moving. Filing the end of it a tiny amount allowed me to tighten it all the way without binding on the bolt.
If that doesn't do it, remove that screw. Underneath it is a pin that goes through the bolt and the lever, linking them. This pin could have backed out and could be blocking the bolt from going back. Put a small (preferably brass) punch in the screw hole and give it a tap or two to drive it back to its fully seated position, see if that works.
If this doesn't work and the bolt is still stuck, it's possible you have a stuck case. If you shot an overpressure hand load, this could have happened. As long as there isn't a live round in the chamber, You could put a long brass rod down the barrel and tap on the end of it as you try to open the lever.
Other than that, I'm not sure what else it could be. If I remember right disassembly requires the lever to be partially open, I'm not sure the rifle will come apart properly with the lever stuck.
I'm sure someone else will chime in with more ideas.
G