Answer:
His Father's Death and the Ghost's Revelation: Hamlet is deeply grieved by the sudden death of his father, King Hamlet. However, his distress is compounded by the circumstances surrounding his father's death. When the ghost of King Hamlet appears and tells Hamlet that he was murdered by his own brother, Claudius (Hamlet's uncle), who has now become the new king and married Queen Gertrude (Hamlet's mother), it shocks and angers Hamlet. He is burdened with the knowledge of his father's murder and the knowledge that his mother has married the man responsible for it.
Betrayal and Deception: Hamlet is also deeply upset by the betrayal and deception he perceives in the actions of those around him. He feels betrayed by his mother for quickly marrying Claudius after his father's death, which he sees as a betrayal of his father's memory. He also feels betrayed by his friends Rosencrantz and Guildenstern, who have been sent by Claudius to spy on him. Hamlet's sense of isolation and his perception that everyone around him is deceitful and untrustworthy add to his emotional turmoil.