Updated WP, JetPack, and Themes this afternoon. Now site broken.

Try manually resetting your plugins (no Dashboard access required). If that resolves the issue, reactivate each one individually until you find the cause.

If that does not resolve the issue, access your server via FTP or SFTP, navigate to /wp-content/themes/ and rename the directory of your currently active theme. This will force the default theme to activate and hopefully rule-out a theme-specific issue (theme functions can interfere like plugins).

Thank you for these suggestions.
I have no idea how or where to install phpMyAdmin, however. Nor have I ever used FTP or SFTP.

I don’t know whether you can help someone at such a beginner level!

By “host control panels,” which might have phpMyAdmin pre-installed, does this mean GoDaddy?

Yes, see:

https://support.godaddy.com/help/article/4881/finding-your-hostingftp-login-or-user-name

1) Using my server’s (GoDaddy’s) ftp site, I deactivated all my plugins, by following the instructions at “How to deactivate all plugins when not able to access the administrative menus?” This entailed changing the name of the plugin folder, going to the dashboard, then changing the name back. I have not reactivated any of the plugins yet.

2) On my server’s (GoDaddy’s) ftp site, I renamed ALL the theme directories (I confirmed I am using 2011 Theme, but all were recently updated). I wonder if I need to UPLOAD the renamed files from GoDaddy, but I cannot. According to the message I receive, my Firefox browser doesn’t support file uploading, and I need to get the Chrome browser. The changes to the plugins happened without “upload.”

Thus, I have tried James Huff’s two suggestions, to no avail. I do not get the error messages when I try to log in, just a blank screen. I do now have access to my dashboard.

Thank you WPyogi for sending me to the right GoDaddy place. I worked my way through it.

I switched to the 2010 theme (most like my 2011), and the site will now come up. The Themes window said the 2011 theme was broken, so I deleted it and reinstalled it and now my site is up and has the correct theme.

I do need to go back and get my sidebar widgets on the right pages and put some photos in, but I think I’m on the way.

Thanks for the help. Now I know about GoDaddy’s FTP access and getting back the dashboard–both of which were essential to figuring out a fix.

Yay – glad to hear it’s back up – and yeah, the widgets and other things should be pretty straightforward :)!