it looks to me the actual metal slot that the screw goes into has broke away from the plastic on the pismo casing. Happened to me a few times with my iBook Clamshells. Fortunately I had 3 extra cases to tray again on. But seeing as how you have stuff in that case, I would try as much as possible to get all your parts out and just get a new bottom or top case witch ever the screw is in and just replace it that way. It is WAY easier to do that.