Stuck for 2 days.

I am playing dead money & have got as far as getting to the vault. Via the Elevator in Veras room !!! now as I don't have the gun for breaking the electronic screens I have to go down the old stairs. thats the problem cant find a route out,#any help or vid link appreciated
Russ

Do you mean the gun that lets you shut down the forcefields?
It wouldn't work anyway.
http://www.youtube.com/watch?v=fsD5r2Ygvy8&feature=channel
Here's a run of the vault.

I do not really understand your issue...

^Thanks Adept.
Cant spot that last detector before the shut off terminal. its killing me literaly . the second staircase with the posion cloud below !!!!!