WP Admin 404 Page not Found error

Hi,

Today when I was trying to login to my dashboard of my wordpress site, the admin page was showing error shown below.

404. Not Found.

This page doesn’t exist.
Go back?

After searching Google for few hours, I finally decided to remove this code from my .htaccess file.

RewriteCond %{HTTP_HOST} ^technicalnotes\.org$ [NC]
RewriteRule ^.*$ http://www.technicalnotes.org%{REQUEST_URI} [R=301,L]

If I remove this code, I can see the admin page at technicalnots.org/wp-admin. But the problem is this will create redundant name issue in Google Analytics as www and non-www version of the website will not redirect to the same page.

And if I put back the code, the web page will redirect to http://www.technicalnotes.org/wp-admin which doesn’t allow me to login and shows 404 not found error.

I did not change anything recently nor installed any plugin for my WordPress site. The site was working fine even with the code fine for a year now. Today, all of a sudden this problem occurred from nowhere.

Any help would be appreciated.