Capgat, I suspect your latch/lock adjustment is out of whack. When you slammed it and it was closed, it probably jarred the latch and now it thinks the gate is open when it's closed. You need to tighten the screws for the latch and verify proper adjustment. If that doesn't fix it, you may have damaged it and ruined it altogether. The latch probably scooted in so far that the depth of the plunger tells the latch that the tailgate is open, try adjustin the latch out a little, making sure it's tight, and recheck. Lemme know.