You didn't touch anything, it worked 5 hours ago, and doesn't work now? Just wanna clarify this...
Check your crons. See if something got "updated" without you doing it. Roll over the httpd.conf and see if anything sticks out (if it does, that's definitely wierd, especially if you didn't do it). Try stopping and restarting apache:
apachectl restart OR
That is really very odd... Is it a permissions thing? Have you changed any permissions? Did an "updatedb" do something to some symlinks?
Just tossin out some ideas...