Look at the trunk latching mechanism and you'll find what looks like a, "C", laying on its side, with the open part of the, "C", facing a rod that it latches to when the trunk lid is closed. If the, "C", is not open, that means it's in its closed position and will not latch because the it can't latch onto the rod. Try moving that, "C", back and forth until you get it to the open position. You might be able to do this with your fingers and if not, gently use a screwdriver to push it back to its open position and then it should latch again.
Good luck with it and let us know how you make out.