You are trying to connect to the database with a user for which a profile was defined.
On this profile a value for FAILED_LOGON_ATTEMPTS was set
You tried to logon with this user but entered an invalid password consequently for maximum number of times specified by the user’s profile parameter FAILED_LOGIN_ATTEMPTS.
Another possibility is that the DBA locked the account.
You will have to wait until the value of PASSWORD_LOCK_TIME has been reached so the account gets unlocked automatically or contact a DBA to unlock the account.
To see what profile is assigned to a certain user, issue following select:
select profile from dba_users where username='YOUR_USERNAME_HERE';
To see the limits set for the profile, issue following select:
select resource_name, resource_type, limit from dba_profiles where profile='YOUR_PROFILE_HERE';
If you want to see which user locked the account, you can use following select.
Be sure that database auditing is enabled and that you are auditing creation of sessions.
select * from dba_audit_session where username='YOUR_USERNAME_HERE' and returncode != 0 order by timestamp desc;
You can use Oracle Password Changer to change Oracle passwords and unlock accounts.