That's a tough one.
The first thing you will have done is switch the motor off. Take the batteries out.
The next thing is to remove the film magazine, so you will have access through the aucillary shutter.
Then it is a matter of trying to unjam the thing using a small screwdriver. Insert it in the small slotted axle end below the lens. Rotate it clockwise slowly, either until things free up and the cycles completes, or until there is a click and the axle locks in fully wound position.
Do not force things!
That may not work, in which case you could try the procedure described
Dead Link Removed.
The other, safer option is, of course, to have a qualified repair shop see to it.
P.S.
I noticed only now that you mentioned that the screw (slotted axle) is firmly stuck.
In that case your should try to move the mechanism away from the lens as described on the linked page.