From the WampServer icon, left click, select Apache > Alias Directories > .../phpmyadmin/ > Edit alias to open the alias configuration file and then changed: 

<Directory "c:/wamp/apps/phpmyadmin3.5.1/">
    Options Indexes FollowSymLinks MultiViews
    AllowOverride all
        Order Deny,Allow
  Deny from all
  Allow from 127.0.0.1
</Directory>

such that the Allow line became: 

        Allow from 127.0.0.1 ::1

That will fix things for phpmyadmin and if you intend to use SQLbuddy or Webgrind then you'll need to make a similar change to their configuration files. Furthermore, if you've modified the Apache configuration (as I had) then you'll to make a similar change to any localhost Allows in httpd.conf too.

http://forum.wampserver.com/read.php?2,110531

To fix the issue with localhost under Windows 8 giving a 403 error (but working for 127.0.0.1) I did the following:

Fix 403 Forbidden wampserver tools (PHPmyadmin, sqlbuddy etc) on Windows 8

apache

Apache