WP Super Cache stopped working; please help

It used to work, now I see this:

1. With caching on I can get to my website in Safari, Chrome, and Firefox on a Mac. But on a PC it does not come up in Chrome, shows Page Not Found.
2. With caching off I can bring up the site in Chrome on the PC and Mac (and the other browsers on the Mac).

I deleted the cache which did not fix it. I turned Caching Off until it’s fixed but my site is much slower without the plugin.

Does anyone have any ideas on how to fix it?