I would try to take the Clamshell apart to the point where you can inspect the hinge mechanisms underneath the top case. I think it could maybe get jammed if the "clutch cover" plastic section between the hinges was improperly aligned at some point.
At the very least, taking the top of the Clamshell case off will allow you to have easy access to the hinges for adding some lubricant. (I think a few drops of silicone lubricant or maybe WD40 ought to do the trick.) I imagine that the metal hinges are a lot more resilient than the plastic components around them, so if you do need to apply some force to the hinges to "un-stick" them, I'd try to keep the force confined to the metal areas as much as you can. If you disconnect the screen from the computer and use pliers to manipulate the hinges, this might help take pressure off of the bottom plastic computer housing.
