!Please Help! Broke WordPress by changing the Blog URL

WordPress experts,

I desperately need your help!

I broke my installation of WordPress by changing the blog URL under settings to

http://www.mydomain.com/index.php

instead of http://www.mydomain.com

Can someone tell me how i might be able to fix this?

When i try to login to the admin it prefaces

http://www.mydomain.com/index.php?wp-login.php and goes to the Not FOund page.