Quick Walkthrough on how to get through the third floor and into the Vault (I think this is what you're looking for):
From the doorway where you enter this
room, on the opposite side of the
room, there's a long enclosure that
runs most of the length of the
opposite wall, plus a very small
enclosure in the right corner. The
doorway to exit this room is between
these 2 enclosures, and one of the
holograms is standing guard next to
it.
There's also a medium-sized enclosure
on the far-right wall that has a
terminal that controls the Hologram
next to the exit. Also, on your right
as you come into the room, there's
stairs going down to a lower catwalk
level. The Cloud is covering this
lower catwalk level, and you have to
jump from the bottom of the stairs to
the next section of this catwalk.
Also note the metal supports overhead.
The hologram emitters are on top of
the supports, but walking on them can
be a little tricky, especially when
the holograms turn hostile and start
shooting you after you take out any of
the emitters. To get to the overhead
supports, jump on top of the far-right
enclosure from the main catwalk.
There's steps leading up to the
supports from the top of the
enclosure.
As you turn the corner after exiting
the hologram room, your collar will
start beeping as you run toward a
speaker on the wall ahead of you.
This terminal lets you deactivate the
weapon turrets and the blue
forcefields around the Vault, allowing
you to get into the Vault. But
deactivating the security also
triggers the entire sequence of events
leading up to the confrontation with
Elijah, including locking the elevator
out of here until Elijah actually
comes down to the Vault. So, switching
off the security is basically a point
of no return.
You'll see 2 folders regarding the
Vault's security. Back out of the
folder and you'll now see a 3rd option
to disable the Vault's security
protocols.
