It is possible that you have not specified directory access in the Apache Config file.
This would mean that Apache does not have access to the document root you have specified.
Open the Apache Config file, and ensure that you have a directory entry for the document
root directcory specified. It should look something like this:
<Directory "C:/webdev">
Options Indexes FollowSymLinks
AllowOverride All
Order allow,deny
Allow from all
</Directory>