Sadness... (depressed rant)

[Kandir]

Not that it necessarily applies in this case, but I thought I would point out that blizzard's method for banning accounts is to change the password. They do this instead of deleting, since it gives them a backup plan in case there arises disputes which require re-activating the account.

So, it could be that your account got banned. That's actually the most probably reason. Hacking into an account would not be as easy as you might think.