Do you run postgres in service or do you start it manually ?
Which system user did you use to create the libresource database ?
If you run it manually you should start it with this command line:
postmaster -D FULL_PATH_OF_DATABASE -i
And you should use the same user login with no password to access to the database...
The "-i" option is needed to allow the LibreSource serveur to connect to the database in TCP.
For the configuration of postgres you can keep the default one for simple demonstration.