[Keven]

Here's a quick way to check if the servo is the problem. Once you have verified that
that the vacum line is properly attached, place your foot on the brake pedal with the
car off, keep your foot on the pedal, and start
the car. The pedal should move slightly down when the car starts, if not you have a dead servo.

Dont think you can rebuild a ATE servo, so if it is out, you'll be out $300!!

John is absolutely right about the brake fluid ruining the servo, it happened to me.
If it is leaking into the servo, a telltale sign is the paint peeling where the bake master
cylinder attaches to the servo.
I no longer wait for the master cylinder to go, I simply rebuild it every 50K miles or so.
Also flushing your brakes out every two years does wonders to prolong brake parts life.