@SSR:
I do not know if this will help, but this is what I would do given the situation you describe:
DO NOT TRY TO FORCE THE SLIDE INTO BATTERY (Closed), this could potentially result in a round jammed in the chamber or a slam-fire.
Instead:
Remove the magazine, and empty it of all rounds, then reinsert the magazine.
Brace the front of the pistol againsts a WOOD surface (one you don't mind scratching), with the edge of the wood against the slide but over the barrel.
Push down on the pistol, and at a slight angle (otherwise the slide could slip off the wood). Be very aware of muzzle direction, in case the slide retracts and slams forward and detonates the round (not likely, but possible nonetheless).
Ideally a steadily building pressure downwards should do the trick, or rushes of force.
When the slide is all the way back, the magazine should engage the slide lock, holding it open.
See pics below (sorry, it's nightime here now).
Hope that helps.
Please let us know what happens.
*PS* inspect your extractor claw carefully once the round is cleared, as well as the bore....make sure the bore is clear of obstructions. Keep the round handy if there are peculiar marks on it, photograph if possible, and please share.
Good Luck!