The Machine said goodbye.
In Season 4, we saw The Machine fight for survival by hiding out in the national power grid, constantly trying to outrun Samaritan and its agents. Eventually, Samaritan figured out The Machine's location and created blackouts to corner it in an electrical substation in New York. Finch, Reese, and Root were able to track it down and pack up its core code in a suitcase computer in order to save it from destruction.
We know the team won't give up easily, and in the Season 5 premiere, they will do whatever it takes to resuscitate what's left of The Machine. But, has too much of its core code been damaged beyond repair? And, if they are able to bring The Machine back, will it be the same as it was?