How to unlock Plesk admin user from the shell console
The default lock time is 30 minutes. Do not attempt to log in until next 30 minutes and it will get unlocked itself. If you make 3 additonal failed attempts to login, this will lock out the users for an additional 30 minutes.
You can manually remove the lock from psa database.
Do the following from the shell console
# mysql -u admin -p`cat /etc/psa/.psa.shadow`
mysql> use psa;
mysql> delete from lockout where login = 'admin';
This short but helpful tip would allow you to login to the admin panel immediately without having to wait for 30 or more mins.