I am just shooting in the dark here but when a car is as old as 15 years the lubricants have collected a lot of dirt and crude in them. I would try to thoroughly clean the hatch latch mechanism with brake cleaner, to see if it frees up and will work. Be careful with the cleaner and protect the plastic surrounding the hatch latch. On my 93 I had a lot of things that were bound up with old lubricant such as the door locks and keys the hood releases the door hinges etc. I cleaned them up and used a silicone lubricant on them. While your at it spray the silicone on the rubber seals for the windows, doors and hatch, and put a white lube on the hood adjustment bumpers. Good luck and keep us informed on what fixes your problem.