Hi Dave,
There are a few reasons that could be happening, and ways to fix them. First, the latest version of WP is 5.8.2, so it should be updated past 5.6.6 as soon as you can get into your Admin panel. Here are some things to try:
1. Check with GoDaddy support. They can likely diagnose and resolve the issue for you. If you’d rather try it on your own, try:
2. It could be a plugin conflict. If you can FTP into your site, go to wp-content folder. Change the Plugins folder name to something like Plugins-2. See if that resolves it.
3. Delete the .htaccess file. It’s a hidden file in your main WP directory, so you’ll need to select View Hidden Files in whatever FTP app you’re using.
4. Look at your wp-config file (download the file first as a backup). Paste this code in that file:
define(‘WP_HOME’,’https://mywebsite.com’);
define(‘WP_SITEURL’,’https://mywebsite.com’);
Fill in the correct URL for your site.
Clear your cache and cookies and try wp-admin again.