the step to remove old plesk before can start install a new
but it is preferable to have a complete system restore..
*** somehow . to wait for sys-admin to do thing to you.. ah.. a lil’ bit fu*ked thing.. why not ***..

as root..
1. yum remove psa-*
2. yum remove httpd
3. rm -rf /var/httpd -R
4. rm -rf /usr/local/psa -R
5. rm -rf /var/www/vhosts -R
6. service mysqld stop
7. If don’t know the root pass for myql .try this as root :
mysqld_safe –skip-grant-table

6. mysql -uroot
i. drop database psa
ii. drop database phpmyadmin_14813SHFF < -- some serial here can see using show databases;
iii. drop database horde;
iv. drop database sitebuilder;
v. and any other thing .. except test and mysql;
vi. may have to reset pass for root to blank ... if u want to delete other user than root in mysql

use mysql;
delete * from user where User!='root';
update user set Password=PASSWORD('') where User='root';
may be need to add the admin user with pass setup.
and with all priv here.
insert into user (Host,User,Password) values ('localhost',admin,PASSWORD('something-default-here'));

then have to grant.. all the privilege. to the admin

then remove mysqld.
yum remove mysql.

***.. after that may proceed with re-installation process.
note i did'nt remove any other user created before.. such as qmail.. bla..bla.. because we are going to re-install
..

then..
./psa_installer_v3.1.2_build070321.17_os_CentOS_4_i386

answer all question.. wait.. till finished..
hopefully no problem..

may be need to flush the firewall
services iptables restart..

then can access to
https://server.name.com:8443/