My bad,I assumed that it didn't continue after the game over and resetted when my party got killed.PLaying on act 1 now,thanks!
Im in the same case excepted for me its after getting the 5th girl.
From what I remember,you have to go back close to your first room,where is the generator(thing that do alot of noise),then the girls will activate the switch by making a human ladder.
The darkened corridor will have light on after that so you can go to main system room(with a big computer)to unlock shower room.
But it doesnt work when you have the 5th girl.And I looked every room,spammed every corner,chest,door by pressing z,have no clue what to do anymore to continue.