It must be assumed that Hemlet is genuinely shocked and horrified by the truths revealed to him when the Grost says:
Now, Hamlet, hear:
'Tis given out that, sleeping in my orchard,
A serpent stung me; so the whole ear of Denmark
Is by a forged process of my death
Rankly abused: but know, thou noble youth,
The serpent that did sting thy father's life
Now wears his crown.
O my prophetic soul! My uncle!
Hamlet has had no hint of evil, but he is a highly Intelligent and intuitive character, and he has sensed that there were suspicious circumstances associated with his uncle's ascension to the throne and marriage to Gertrude. Hamlet has known Claudius all his life and has probably never liked him, although his uncle has probably gone out of his way to win his nephew's trust. When Hamlet is left alone, he says to himself:
O villain, villain, smiling, damned villain!
My tables,--meet it is I set it down,
That one may smile, and smile, and be a villain;
He thinks of his uncle as a man who is always smiling. No doubt, Claudius has been smiling at him ever since he was a little boy--and yet he has never liked the man. Smiles are often meant to disarm us. Villains do not declare themselves as such. In fact, what characterizes a villain, in Shakespeare's time as well as our own, is that he takes great pains to hide his character behind an innocent facade. A person who is evil and doesn't try to hide it would not be considered a villain; a villain has to be somebody who pretends to be something other than what he is.
So the most that can be said about Hamlet's prescience is that he sensed intuitively that there was something suspicious about the abrupt change that had taken place at Elsinore in his absence but that he did not know what it was. Claudius continues to smile and smile at him, but the usurper is consumed with guilt and fear; he is afraid that Hamlet suspects him of murder or else that Hamlet will put two and two together and figure out the solution to the puzzle. In that case, Claudius knows that his own life would be in danger. Throughout the play he is trying to pry into Hamlet's mind to fiind out what he is planning. At one point in the play Claudius tells Polonius, in one of Shakespeare's marvelous and characteristic metaphors:
At the end of Act 1, Scene 2, after Hamlet has been informed about the appearance on the battlements of a Ghost resembling his deceased father, he says to himself:
My father's spirit in arms! all is not well;
I doubt some foul play: would the night were come!
Till then sit still, my soul: foul deeds will rise,
Though all the earth o'erwhelm them, to men's eyes.
It would appear that he only begins to suspect "some foul play" because of the arrival of his father's Ghost, and that his previous ill feelings about his uncle and his mother may have been the result of natural resentment for being cheated out of the throne and revulsion by his mother's licentious behavior. The Ghost's revelations come as a complete surprise. He is young. He could hardly have imagined there could be so much wickedness in the world. His new knowledge makes him see all of humanity in an entirely different light. Reality is not the same as what is taught in school. He has read many books in many different languages, but now he thinks they are nothing but words, words, words.