As you do, a bunch of not-zombies will rush into the room.
Make sure Ashley is safe near the door to the east (the same door you used to enter the room) before you unlock the door to the room. Another guy will run over and lock the room, so take him out as well. When you've killed the first couple of enemies, run forward with your shotgun to quickly blast away the crossbow enemy.
If you can get far enough around the corner, you should be able to use the wall as a shield against the crossbow shots while you first deal with the other not-zombies. There are a few enemies just around the corner, including one with a crossbow that likes to take cheap shots.
As soon as you enter the next room, back up a bit and get Ashley behind you.
