Forbidden You don't have permission to access /wp-login.php on this server

The solution is to add this to the beginning of your .htaccess

<Files wp-login.php>Order Deny,AllowDeny from allAllow from all</Files>

It's because many hosts were under attack, using the wordpress from their clients.

I had this same problem, and after temporarily deleting all my .htaccess files, then trying to modify them as suggested, and making sure all my files and folder permissions were set to 777, I still couldn't get it to work. I don't know why I couldn't access the file, but I was able to create a new file and access it no problem. So what I did was create a new file in /wp-admin/ called temp.php and pasted all the code from install.php into it. This allowed me to access the file. The only other thing I had to do was edit the code so that the form submitted to temp.php instead of install.php. After that, I could finish the install and everything worked.

<form id="setup" method="post" action="temp.php?step=2">

Make sure the following lines are not in your wp.config

define( 'FORCE_SSL_LOGIN', true );define( 'FORCE_SSL_ADMIN', true );define( 'DISALLOW_FILE_EDIT', true );

I got locked out after deactivating iThemes security plugin