'I have no mouth, and I must scream' is a short story by
Harlan Ellison. It is a little under 6,000 words long and won the 1968 Hugo Award for shortform fiction.
It is set in the future, after an atomic catastrophe has devastated the Earth. Humanity has been reduced to a handful of survivors who are kept alive by an insane computer, called AM. At one point AM is described as speaking with a voice which sounds like 'the shriek of babies being ground beneath blue-hot rollers'. This is a very Harlan Ellison thing to say, and one of the reasons why people like him so much.
AM is keeping our heroes alive so that it can submit them to hideous torture for all eternity, because it is bored - bored, because the apocalypse has destroyed everything in the world of interest. The story has perhaps the ultimate bitter-sweet ending; the title is the last line of dialogue, delivered by the main character after offending AM for the last time.