Our Admin Login issue got fixed. Along with this issue, the Customer side also had an issue. You couldn't "Add to Cart" anything. Buy Now continued to work but nothing could be "add to cart" .. the cart remained empty.
It all started when our SSL certificate renewed AFTER we had in IP change. On the day of renewal, no more logging into the Admin part of our cart. And no more "add to cart" functionality.
Our hosting server support people spent all week insisting the SSL renewal was good, had no issues, created no issues. Until today. I finally got one that really looked into it. They discovered there needed to be a new update to the htaccess file.
Poof! All issues corrected.