It's been like this for two days now.
Noting that when I cleared my browsing history/cache/cookies in Chrome, I was able to access my site again in that browser. I haven't done the same for Firefox, but I plan to soon.
Thanks for the help. My error log has several entries for the following two errors since Dec. 26:
[26-Dec-2013 20:34:37] PHP Fatal error: Class 'ANTIBRUTEFORCE_BOL_Service' not found in [URL omitted by me] /social/ow_plugins/smartcaptcha/controllers/smart_captcha.php on line 85
[28-Dec-2013 17:08:42] PHP Fatal error: Call to a member function getEmail() on a non-object in [URL omitted by me]/social/ow_plugins/quicksignin/components/recent_login.php on line 59
It came up for me as a blank page to.
Quick fix.
Go to Tools . Compatibility view settings and then add your site and press close.
Page will reload and work. Be sure also in internet options to uncheck "Clear history on exit" as this will wipe out your compatibility site settings.