Ok,
Do this first and foremost.
Remove the nitrous line from the intake tract. Have someone hold it up in the air and go inside and push the button.
If nitrous does not blow out then you could have a solenoid problem.
Reason I feel this way is years ago I had the same problem. Got to the track and the car didnt perform any over stock and as I was under the hood clicking solenoids a buddy told me to disconnect the line and see if it shoots up in the air (like a purge)
I did it and even though the solenoid clicked repeatedly ,,,nothing got through and therefore I didnt spray a damn thing.

Just a thought , but you should definately feel a 75 shot.