Fatal error: main(): Failed opening required

I’ve just installed WordPress 1.5. But can’t connect to my data base at localhost. I’ve checked and rechecked my data base name, password and user name, and they are all correct. Help, please… Karl

This is the warning I get when I attempt to run wp-install.php
Warning: main(/home/xxxxxx/public_html/blog/wp-includes/wp-db.php): failed to open stream: No such file or directory in /home/xxxxx/public_html/blog/wp-settings.php on line 30

Fatal error: main(): Failed opening required ‘/home/xxxxx/public_html/blog/wp-includes/wp-db.php’ (include_path=’.:/usr/local/lib/php’) in /home/xxxxx/public_html/blog/wp-settings.php on line 30