Get to the end of the tunnel. To the left you will find another passage. Crouch and walk through it.
When you get rid of all the enemies, examine the room, you will find some goods. Then walk down the stairs and turn left.
You will encounter a very fast zombie. Kill it. If you're fast enough, just shoot at the barrels right behind him.
Keep going and watch out for zombies and barnacles. Use the red flammable barrels to kill them.
When you get to the room with generator, you will have to kill a zombie that will carry a grenade. Then look at the pipes on the left. There's a crate with goods.
Then go straight and up the stairs. Mind the gun on the crate. You will get to a ladder with a zombie cut in half next to it. Climb up.
You will get on a roof. There will be some metal sheets. Remove them and try to kill every zombie you can. Then, get inside.
When you are inside, you will hear some music. That means you will have to clash with zombies. Take out the shotgun. Try to avoid zombies and get them in the places where Alyx will have a shot. Use the shotgun only when it's inevitable. The ammo is too precious.
When the music is over, kill the rest of the zombies and go into the opposite direction to the laser beam. There are some goods. Then go to the right and inside a tunnel. (A door is lying there).
You will get to a room with a fence. Crouch and get inside the tunnel.
Keep going and watch out for headcrabs. You will get to a room with barnacles. Use the gravity gun and the red barrels to kill some of them. And then use your gun.
Collect the goods and kill crawling zombies. Then jump on the platform right to the red lamp.
Climb up until you get to the highest platform. Get down. Find a big locker and try to push it on the pallet that is on the forks.
There's a red lever on the forklift. Move it by pressing the action key. The pallet will start going up .
When the pallet stops, get back on the highest platform. Then use the pallet to get to the other side.