People don't just get locked out of their accounts - for someone to get access to your account, they need your password. If your password is even decently strong, then there's no way someone is going to guess it. For someone to get access to your account AND your bitcoins, they need your password and your PIN. Again, if those things are sufficiently strong, no one is going to have guessed them. Assuming your password and PIN were strong, that leaves the following possibilities: 1. you were entering these incorrectly; 2. at some point, you entered them in a phishing site; or 3. your computer is compromised somehow (keylogger,etc.).