The codes required for the computers are as follows.
acd
bcd
abc
adc
bac
dca
dcb
abd
acd
bda
Easy completion in Ruins
You will need a four digits code (1574) to operate the large cargo elevator to complete the next objective. You will eventually be instructed to retrieve the four digit code. Once you get to the lower floor (basement), use your laser gun again to interrupt the barriers to complete your objective. Climb the ladder on your right. Walk on the narrow edge of the wall where the laser barriers are located. The best way to do this is with your back against the wall. Fire and restore your laser gun when needed. You can also touch one and it will knock out all the laser barriers in that area, and will also give you an extra laser to fire. In order to make your final escape you will need speed, avoid fighting enemies, and timing. You will only have less than four minutes to escape. Make your escape by going up to the rooftop. There will be stairs that you must climb and small rooms that you will be going in and out to reach the stairs. Keep going up until you see the weapon resembles a lightning rod on the left and stairs on your right. Run pass that weapon. Avoid the enemies and you will see a ramp attached to the machine. Go up to it and press [Use]. Go up the stairs and enter the elevator. On your way to the next level you must jump up and crawl to the next ramp. Keep going in the up direction and you will see another lighting rod like weapon to your left. Repeat the same steps as done previously. Once you reach the top, pick the door to escape.
Elevator code in Asylum
On the Asylum mission, there is an elevator. The code for the elevator is "4747". You can get the code by talking to Neil Caplain, who is located in one of the padded cells.
Fire alarms in Embassy
When at the end and you have to turn on all the fire alarms, one of them is in Basement 2. Note: After you turn on all the alarms you must hurry to the ballroom and fight three men, then find Dixon and escape.
Getting DNA in Asylum
When you are trying to get the man's DNA and must follow him, once you get in the room with all the picnic tables go to the right side of the door and stand there. He will walk by time after time until you get all of his DNA. You will then fight him, escape from the Asylum, then move on to the Embassy level.
Laboratory
Use the following steps when in the lab and cannot get the prisms. Next to the giant laser is a tall box that is big enough for you to fit inside. Jump up on top of it. There is a pole directly above it. Climb onto the pole, then go all the way over to the elevated part (with computers and and other objects). Jump down. There is a computer by itself in the corner. Hack it. The gun turret will then turn off. Run down the stairs and get the prisms. Someone will start coming towards the lab. Run over to the laser and put the prisms into it. Then, run over to the tall box and get inside. The door will shut. Stay in there until it is safe to exit (after the enemies are inside the lab). Jump out of the box and defeat the two men. Then, save Agent Jacobs. Use the laser to blow up the things on the wall near the tin shutter object. Note: There is one outside and another inside. Then put the toxic material into the fuel cell and exit.
Replenish heath
If your health is low and Sydney is breathing like she is tired, get away from all targets and wait for awhile. Her health meter will go back up. Note: This may take awhile.
Computer codes...