In the Ruins Mission you need a 4-digits code [1574] to operate the large 
cargo elevator to complete next objective. You will eventually be instructed
to retrieve the 4-digit code. Once you get to the lower floor(basement) you 
will have to use your laser gun again in order to interrupt the barriers to 
complete your objective.

Climb ladder on your right, you will have to walk on the narrow edge of the
wall where the laser barriers are. 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's barriers in that
area and also give you an extra laser to fire.

In order to make your final escape you will need speed, avoid fighting the
enemies, and timing. They allow you less than 4 minutes to escape. You will
have to make your escape by going up to the rooftop. There will be stairs 
that you have to climb and small rooms that you will be going in and out 
to reach where the stairs are at. (#1- Keep going up until you see the 
weapon that look like a lighing 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 the (Use Button-is to allow you enter
elevators). Now head up the stairs and enter elevator. On your way to the 
next level you will have to jump up and crawl to the next ramp, keep going
in the up direction and you will see another weapon (lighting rod) to your
left again, so you repeat the same step #1. Once you reach the top, a door
that you will have to pick and unlock to escape.