Why did Harry have the worst birthday in Harry Potter and the Chamber of Secrets?

Answer 1

Harry had hoped that his birthday might be different given that he had made friends at Hogwarts, but because Dobby was stopping his mail, he didn't get any cards from them. The Dursley's also completely forgot his birthday.

Then, Dobby tells him Hogwarts will be a dangerous place, before getting Harry in trouble with the Ministry and the Dursley's who, know that they know he can't turn them into frogs, decide to lock him up in his bedroom.