Admin Login Issue

Hello, I’m trying to help a friend that has tanked his site. I don’t have a lot of WP experience but I’ve had my eye on it for a while.

In attempting to login to the dashboard using the “wp-admin” extension, this is all that we get:

Not Found

The requested URL /wp-admin was not found on this server.
Apache/2.2.15 (CentOS) Server at (site).com Port 80

Does anyone know where I should begin looking. The htaccess file is blank. Should it be?