Starting cell
Look around in the drawers, grab the goodies, mainly light stick and coin, put the coin in the workbench's pressure crusher and turn the wheel. Now there's a vent on the wall, use the flattened coin on the screws holding up the vent.

Vents:

Go through the first vent section and come out, put the coin in the soda machine, grab the soda. (You can also get the soda can from the machine by grabbing a rock and throwing it at the machine) Continue your vent exploring on the other side of the collapsed potion. There's a tricky part here as part of the vent will break if you walk on it, instant death. Grab a piece of wood from the debris and lay it on the weak portion, continue to the Freezer. In the Freezer, use the soda on the thermostat, which will disable the steam and open up the rest of the vent passage, get back in the vents and continue through the now open passage.

Foyer and storage rooms:

There are lasers protecting 2 sets of doors here and a dead body. Grab the 2 barrels on the right side and pile them, jump over the lasers. Clear the rubble on the right hand side of room and go through the door, go straight ahead and enter the first room, grab the stuff scattered around the room, make sure you get the alcohol, get the tape and listen to it. go further down the hall, there an fuse box, just behind you there's a small pile of rubble, grab a piece and smash it against the box, it opens it up. Pull the wires, it shuts off the power and opens the storage locker room. Go in the room, grab the syringe and crouch behind the table, an infected will come, stay where you are and listen until the infected does his rounds and leaves. Leg it back to the foyer.
You might need to turn off the lasers here, unless you want to pile some stuff and jump over them. To turn off the lasers, fob the C4 box, a panel will come up, you need to set all nodes to red symbol, click around and you'll eventually get it. Combine the alcohol with the syringe to clean it then use the syringe on the dead body. Then use the syringe on the door with the biometric scanner. Presto you're in.

Mess Hall:

Turn right and go into the room, drag the heavy barrel in front of the open fusebox and throw the switch, the sparks will light the barrel, the fire alarm will go off and you can enter the locked door ahead. There is a welcome CD to grab on one of the tables. Continue straight and go left, open the door and save your game, use the CD on the computer, read the text files and run the door un-locker file and unlock the door. Go through the drawers and grab the flash light and batteries.
Go back into the mess hall and open the previously locked door on your left. Move the box and go underground. Go straight until the drainage room, turn the valve.

Dream Sequence:
Move the chest under the table; put the soup can on the shelf. Then put the dead dog on the open hands, go through the warp-hole.
Puzzle room #1
Fob the arms on the walls so the ones you "activated" continue to flame, it's easy to figure out the combo that will open the door.
Puzzle room #2
Move all the barrels to cover the same number of matching colored lights, flip the switch.
Puzzle room #3
Go up the ladder, flip the switch, go back down the ladder and look up, flip that switch, door opens.
Puzzle room #4
Jump on the moving platforms to make it to the other side, get in and shut the door, pile up barrels to make it across the barriers. Leave the room.
Sewers:
Jump in the water and move the boxes to form a walkway, climb the ladder and go to the other side, pile up some boxes to reach the sewer exit on the ceiling.

The Facility:

You end up in the sleeping quarter. Swap the fuse in the box ahead of you to be able to boot the computer, use the computer. Head for Armory and grab the saw, head to the Computer Room.

Computer Room:

Grab the manuals. Put the saw in the drawer next to the locked door near where you came in. And infected will break out. Run like hell to the back of the room and open the server room door, let the infected follow you inside, get out and close the door. Look around the room where the infected was and grab all 3 circuit boards. Head back to the back of the room and start programming the cards. Here is the list...
blue:
Antivirus
Firewall
Socket Protocol
Circuit Setup
Net Locator
green:
Admin Tools
File Streamer
CMD Interface
Circuit Setup
red:
Disk Info Setup
Hardware Locator
Circuit setup

Use the computer and unlock the infirmary door (the specific door code in your "To Do" list). Now leg it to the Storage Room.

Storage Room:

Disable the lasers, stack boxes on the scale beneath the big metal crate, the crate will crash down, stack items to be able to jump on top of the crate, go in the room and grab the gas mask. Get out of the storage room and run to the Machine Room.

Machine Room:

Put on the gas mask, follow the corridor, grab the metal bar from behind the barrels, break open the metal door using the bar, keep following the corridor, go in room and use the computer, run the valve control app to set one of the
valves to manual control and disable it. Go back and shut off the valve, you can remove the mask now. Go back further into the machine room and open the shut door with the biometric scanner, a worm will start breaking holes in the wall, avoid it by hiding around the power transformer wait for the right moment as the worm chews through the holes, hit the switch, it will get electrocuted and spit out a hand: Grab it and leg it to the Infirmary!

Infirmary:

Grab the wrist strap from the couch on the left side, rummage the rooms, grab the unknown chemical and mix it in the syringe, use the wrist strap and use the syringe, use the hand scanner, the cryo chamber will open up, go in and flip the switch on the left, a container will open up, rip out the head from it and collect it. Now you are ready to go to the library, GO!

The Library & Outside:

Crouch and turn left, look on the book shelves on the left and you will notice a book sticking out, use it and a secret room will open, grab the items and use the switch. Go outside and look around the shacks; you will need to find these 3 items: lighter, spray can and cloth the snow bridge will collapse so use the rocks on the ledge of the wall to make it back. Use the lighter on the barrel in the shack to warm up otherwise you die from cold. Combine the lighter with the spray can and use it on the bridge control lever. Continue to the other side, move one of the barrels in front of the blocked door, use the cloth on the barrel and use the lighter on the cloth, run to a safe distance. Go into the opening to the second part of the facility.

Facility Part 2:

Head down straight, this has a few infected patrols, I prefer to just run past them. Head to the Kennels.

Kennels:

Go right, grab the metal boxes and stack them in front of the 2 dug openings on the walls, go into the control room on the left and fob the switch on the wall. Go back near the entrance and continue to the left wing of the kennels, notice the lights cycle, time your run and stay under the lit lights until you get to the end of the room, grab the Key Card from the dead body and make your trip back the same way. Leave the Kennels, there is a new patrol up the stairs, make it past him and head for the Research Room.

Research Room:

Go into the first door ahead, an infected will chase you around the room, on the right side corner of the room there's a switch and valve, spin the valve and distract the infected until she's under the box and pull the lever, the box will fall and kill it. Grab the key and use it on the locked room, use the computer and unlock the chemical room airlock. Head to the chemical room.

Chemical Room:

Put on the gas mask, use a rock to break the rusty pipes, replace the pipes with the good ones scattered around the room go into the airlock. Take a right, there's an infected that just stands around here, go grab a barrel and toss it to distract him so the infected moves a bit then you can hit the switch he's standing next to. Run to the door that just got unlocked.
The next section is protected by green light security cameras, the idea is to find a switch and use it to open the next set of locked doors. If you get caught you need to go back and enable the switch again. It's easy to get past this section; there are 2 sets of rooms like this. After the 2nd room, leg it
past the hallway and block the door by moving the big rack on the left in front of it. Grab the empty container from the floor and insert it on the left corner of the protected chemical container. Use the control levers to move the mechanical arm to grab the chemical and move it to the furthest left corner, drop it in the container and add it to your inventory. Use the lever on the right side of the room to open the airlock on the left side, run out and negotiate yourself through the steam releases, engage the valve and head straight out to the Examination Room.

Examination Room:

Rummage this room for the required chemicals, there are five of them scattered everywhere in racks, behind shelves, move the picture frame to gain access to the vents. Once you have collected the chemicals, use them all in the mixer; use the research chemical you got from the chemical room in the bottom left side. Mix the chemicals in this order:
214653. Keep in mind the bottom mixer row buttons are reversed.
You need to leave this room now, go back in the vents a dead body will revive and chase you around, you are safe in the vents, wait until the zombie goes into the adjacent room to make your exit, sneak out and displace the metal box blocking the door, you may need to make two trips for this as he might catch you if you are not fast enough.

Trial room #1
Move the stone on the bottom of the wall to your left, grab the metal bar and use it on the opening, in a moment the door will open go out.

Trial room #2
Follow the maze to the end wooden door, take a right, use the switch, the bell will ring and the NPC will break it down, go through it.

Trial room #3
Go straight then left, grab the stone and bring it back to your starting point, put it on the marker on the floor marked "I" go in the room that just opened, use the switch, drag the stone into this room and put it on the marking on the floor marked "O". Continue walking through the maze and go straight through the fire trap. When you are revived, continue going through the doors, the trials end.

Examination Room redux:

Use the computer to write the letter, when he cannot finish the letter, examine (default key: right click) the objects on all four sides of the room,
the walls will start disappearing and the game will end