Do you have an index.html, index.htm, index.php, or other similar file, or is your server configured to direct users to another file? Example, which should be in your main config file:
DirectoryIndex index.html index.cgi index.pl index.php index.xhtm
Apache defaults to looking for index.html and a couple other files, and if there isn't one it's looking for, it'll either give you an error or a blank page (usually it will error, but not always). Another likelihood is that (especially if you're using a php or alternative file format, that either a module isn't set up correctly, or there is an error in the page coding, leaving the web server displaying nothing at all. Also, though not directly related, is that your server's error handling isn't set up correctly, so instead of giving you an error, it's just leaving you with a blank page to stare at.
Obviously, start testing on your server (localhost, through a browser on that machine, lynx is good for a non-gui server), to see if you can access the files from there, and work your way outwards. If you're using something like PHP, you might even want to test the pages for errors using php's console-based program (which you might have to install separately).