I didn't create my own error pages or anything, though. The installation intructions said that if I installed Apache correctly, the server would run (ok) and the default Apache web page would display when I typed http://localhost/ (not ok).

It is not an error page that won't display, it is any page. I also tried installing PHP (ok) and tried viewing a PHP page from localhost (not ok).

The server says it is running fine, so I am not sure what is wrong...but something apparently is...