Go to the Login Help page. This will let you reset your password by sending it to your key's email account. If you don't receive the email after 10 minutes or so, check your spam filters.
If someone has stolen your account by guessing your password, and the above method does not work, then they may also have changed the email address associated with your account. If this happens, contact support to get the email address reset to its previous value. And use a more secure password in future!