Oh! Also...
The same thing that goes for might have (might've), goes for may have, should have, could have, would have.
Or in other words... may've, should've, could've, would've.
Naturally, this also means there's no such phrase as "wouldn't of" and the like. It should be "wouldn't have", which as you might have guessed, is short for "would not have".
Linkin Park did NOT exist when Harry was four years old. So... Either you forgot that Harry was born in 1980 and that in 1984 the members of Linkin Park were probably still waiting to hit puberty -OR- you only included a mention of Linkin Park in the story because you like them enough to either ignore the timeline or actually CHANGE the entire HP timeline just so you could include them...
This is why people HATE it when authors include mentions of current bands, shows, songs, movies, foods, videogames, etc. in HP fanfiction. When they read that Harry is listening to Linkin Park, Blink182, Fall Out Boy, or any other band whose members were still filling diapers when Harry was a kid, they don't think "Harry must like that band", what they really think is "The author is a putz for using Harry to tell me what his/her favorite band is." Because they really didn't sit down to read about you, they sat down to read about Harry. Sorry if that sounds harsh, but there it is.
Don't switch from past to present tense, like in the last few sentences. It's bad.
What are the odds that the Goblet of Fire book being mentioned was actually relevant to the plot and not an attempt at humor?