Visiting admin brings up the installer
Sounds like it's viewing the DB as being empty. The access credentials are correct (it's technically connecting to the database), but it's not seeing any tables in the database.


Does your site use a prefix (ie: craft_) before the database tables? Check to make sure that the prefix specified in config/db.php matches the actual table prefixes.
Double-check to make sure you're connecting to the right database.