WAMP server not processing index files (shows directory listing instead)

Suddenly WAMP decides to give me a directory listing instead of processing the index files. For example if I go to http://localhost, it gives me a directory listing then I can click index.php and it will load.

But as for my dev sites, they are on wordpress and simply clicking the index file does not work in this case. Any ideas on what may have gone wrong where it doesn't seem to be processing the files properly? It was working yesterday and haven't changed any settings, so I'm at a loss