I imagine you've gotten past there by now... but basically, you go down the first ladder, walk across the one walkway, up that ladder, and continue across in the same direction. At that point you're next to where the tanks come out, and there's an ammo crate there.
Then you walk away from the wall and turn right, walk along there and turn left... as you go forward, that's where the quantum guard appears and shoots at you. At the end, you climb down the ladder, and he appears and shoots at you again.
From there, you basically keep going wherever you see guards. So towards the exploding barrel (the only way you can go), turn right and go along there, turn right again, along that walkway, and up the ladder there. Go along the walkway the guards were shooting you from, and then down the ladder... and from there, you just go along the walkway towards the wall, where there's a ladder that goes up into the control room where there's that nice, big, obvious button to push!
So if we use F=forward (usually the only direction you can go), and D=down, U=up, L/R=turn Left/Right, starting from the top of the first ladder, you go:
D,F,R,F,U,F,L,F,R,F,L,F(Quantum guard),D,F,R,F,R,F,U,F,D, towards wall, and Up, and you're there... assuming my memory serves!
Though I'm not sure if you mean *after* you push the button and the tank comes out of the door in the wall that opens up... After you push the button, you have to go out the other door in the control room, since the one you came in gets locked... That's where you're attacked again by the quantum guard as you walk down that hall.
Once you go out the door there, you can hand around and kill the other guards that zoom around if you want... but then you have to go down the (only) ladder, and walk down the only direction you can go (away from the wall) and there's a down ladder there, but it doesn't extend all the way down to the floor till you walk right up to it! (so if you saw it and figured it didn't go down all the way, so didn't bother to try to get on it, you might not have gotten close enough to trigger it dropping down to ground level!)
Cheers