You'll notice a wall with a lamba decal on it. You have a crowbar but can't break the wall YET! All you have to do is kill the zombie and interact with the radio. Then you can break the wall. One swing should break it.

Work your way upstairs and between the wall and the closet, there will be a key. After reaching the key the floor will break and you'll fall. Defeat the zombie and look for the key on the ground.

Where did my crowbar go? It was stripped from you as you entered the garage. To beat the garage boss, pick up the crate in the corner. Wait till the boss swings at you, then hold the crate in front of you. The boss will miss you and smash the crate open. Pick up the magnum from the crate and shoot him.

To get this ending, in the 2nd boss fight with the antlion guard; look for a button. Press it and continue with the fight. Watch out for the roller mine though.
After leaving the arena, look at a brickwall that is broken.Walk through it and open the garage door (which is unlocked now). Head to the door at the bottom of the stairs where you'll get a messge saying you got the good ending.

After you defeat the antlion gaurd, open the door at the end of the alley and kill the zombies. After killing them, metro police will enter the room, take them out and head into the ritual room.
A fire will light and you have to investigate it. Then zombies will surround you.