Twitter locks a user account for about an hour after too many failed password attempts. Like many sites, Twitter does not want to provide unlimited attempts for intruders to crack passwords, so it temporarily shuts down the account for security reasons.
If you have found (or finally remembered) your new password, try logging in again on the Twitter website. If your account is still locked after an hour, disable any third-party Twitter apps like Hootsuite, in case they may be trying to check your account with an old password and triggering the lockout.
If you still cannot remember your new password, you can request a new one from Twitter; check your mail program’s spam filter if you do not get the password-reset message in a reasonable amount of time.
Twitter also has a list of troubleshooting steps if you cannot remember certain things about your account, (like the email address you used to sign up for it) or if you are still having trouble logging in after the password-reset link arrives in the mail.