After install magento, admin page shows 404 page not found

Open your phpmyadmin from your host try once this sql command.

Run this Sql :

SET FOREIGN_KEY_CHECKS=0; UPDATE core_store SET store_id = 0 WHERE code='admin'; UPDATE core_store_group SET group_id = 0 WHERE name='Default'; UPDATE core_website SET website_id = 0 WHERE code='admin'; UPDATE customer_group SET customer_group_id = 0 WHERE customer_group_code='NOT LOGGED IN'; SET FOREIGN_KEY_CHECKS=1;

Now admin can able to login.