I have installed and unzipped Civi in WordPress plugins directory, CiviCRM installer page is blank?
If you haven't already done so, login to your WordPress site with Administrator level permissions.

In Admin, Go to plugins section and activate the CiviCRM plug-in.
After that, open a new browser window and enter and run the following URL "http:///wp-admin/options-general.php?page=civicrm-install

You should then see the Installer screen where you can follow the given instructions.
Hope that helps.