Could not having index.php as default page make applications fail?

I am experiencing various problems relating to default page in IIS7. I am using PHP and ASP.NET at the same time, and for some reason, it doesn't register my index.php in IIS7.

Some of my applications fail to login, in instance, I couldn't login to my WordPress. I couldn't log in to phpmyadmin. Whe开发者_C百科n I try to log in, it just hangs, and won't let me do anything else.

Could this be an issue, or I don't know what's going on.

EDIT

when I say it "hangs", I meant, it seems to load forever... no errors, until it times out. no response back from server.

Yes it could be an issue, sometimes, a PHP application redirects you to a folder, not to a php file.

E.g.: Wordpress will redirect you to http://localhost/wp-admin if you want to enter the dashboard, it is a folder, so the wordpress is expecting the index.php file to be executed, while IIS will look for a default.asp file to execute. What happens here? 404 error.

I hope I explained well...