Why do I write?...I guess because I always have. May seem like a stupid answer, but it's just a normal thing for me. Thinking about why I do it is a little weird, actually. It's kind of wired into me. It's not like I don't enjoy it, or love it, but I just do it because I do. Don't really want/need a reason.
Inspiration is tricky. A lot of the things I think of sort of appear in my head without any previous trigger, but sometimes certain movies I watch will make me want to write to a certain genre, which then leads to a certain idea coming forth, etc. Same goes for books. Music is also a huge influence--if I'm in a crappy mood, I'll listen to the Deftones and probably write something depressing. If I'm in a good mood I'll probably put on the Pride and Prejudice soundtrack and get some sort of romance story after I'm done.
Sometimes rain is helpful. It's a little weird, but I can't write during the day, only at night, and it's always better when it's raining outside. If I ever wanted to be a novelist, that would be a challenge.