1. Open the door and you should be at the room with the cabinet.

2. You should see a plank of wood next to the barrier closest to where you came from.

3. There shuld be a line leading from the plank to the piece of metal or wood.

4. Follow it while crouching turn around when you hit the metal.

The zombies should be in front of you, trying to get to you, but they can't hit you.

Tip: always open the door downstairs in the mystery box and have someone down there, he will kill the zombies that form there if the zombies don't stay upstairs.