permission also. Give your postgres user permission to create database

1 sudo su  postgres

2 psql

3 ALTER USER odoo WITH CREATEDB;

4 \q

5 logout

6 restart server

Please try using Master Password: admin

You will need to create a postgres user: by default the only user is postgres, and Odoo forbids connecting as postgres. 

on Linux, use your distribution's package, then create a postgres user named like your login

Because postgres only allow the login if you have the same distribution user. 

check the user permission also. Give your postgres user permission to create database with ALTER. 

To do this 

sudo -i -u postgres

psql

create user your_user_name;

alter role your_user_name with superuser createdb;

Please check your log file and post it here.

Your postgresql user that you're running Odoo with doesn't have database creation permission.

ALTER USER odoo_db_user WITH option CREATEDB;

Not at a Current Master password, please try to admin as default password..

To change master password, edit

/etc/openerp/openerp-server.conf

Set value for

admin_passwd