Remove the molding from the wall closest to the problem area using a crowbar.
Unlock all the boards leading up to the problem board so you can access it. Lift the boards up and pull out to release them.
Remove the board that keeps coming unlocked and inspect it for damage. Look along the locking grooves to see if it is broken.
Fix the board if possible by removing any rough edges or gluing a broken piece together. Use a thin line of laminate glue to repair any damage on the board. Wait for it to dry and cure completely, otherwise the boards will glue together and won't unlock again.
Vacuum the board's edges and in the opening to remove any dirt that can prevent the board from locking. Click the board back in position and see if it fits snugly in place.
Replace a damaged board that can't be repaired.
Reinstall the other boards and the molding.